A Guide To VRLA Battery Formation Techniques

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A Guide To VRLABattery FormationTechniques


Mike Weighall is an independentconsultant with 36 years’ experiencein the battery industry. He obtainedhis Chemistry degree from theUniversity of Manchester Institute ofScience and Technology. He hasspent most of his working career

associated with the battery industry, in a range oftechnical and managerial roles with major UKemployers, including Lucas, Crompton, Cookson, andENTEK International. In recent years he has played animportant role in the ALABC (Advanced Lead AcidBattery Consortium) as Chairman of the EuropeanTechnical Committee, member of the ResearchManagement Team, and currently Chairman of theProject Advisory Team on Separators. He has previouslywritten the “Battery Test Guide” for Digatron/ FiringCircuits. He has presented nine papers at InternationalBattery Industry Conferences, four of which werepublished in the Journal of Power Sources.

M.J. WeighallMJW Associates12 Low StobhillMorpethNorthumberlandNE61 2SGTel: +44 1670 512262Fax: +44 870 056 0376Mobile: +44 7977 459819Email: [email protected]

© 2001 Firing Circuits, Inc.

Printed In U.S.A., All Rights Reserved

A Guide To VRLA BatteryFormation Techniques

By Mike Weighall and Bob Nelson

Bob Nelson is an independentconsultant with over 23 years’experience in the VRLA batteryIndustry. He obtained his Chemistrydegree at Northwestern University in1963 and his PhD in AnalyticalChemistry/Electrochemistry at the

University of Kansas in 1966. After spending 11 years inteaching and research at the university level, he joinedGates Energy Products where he worked for 13 years invarious positions dealing with the development andmanufacture of both spiral-wound and flat-plate VRLAproducts. He has also worked with other specialty VRLAproducts during work tenures with Portable EnergyProducts and Bolder Technologies. In between, he spentthree years with ILZRO, where he was responsible fororganizing and managing the Advanced Lead AcidBattery Consortium. In addition to the publication ofsome 39 refereed papers, two book chapters and 22invited presentations at national and internationalconferences during his academic career, he haspublished 42 papers and given 41 presentations onVRLA battery technology over the past 23 years.

Dr. Bob NelsonRecombination Technologies909 Santa Fe DriveDenverColoradoCO 80204Tel: +1 303 573 7402Fax: +1 303 573 7403Email: [email protected]


1. Introduction ....................................................................... 1

2. Plate Formation vs. Jar Formation .................................. 2

3. The VRLA Formation ProcessJar Formation ........................................................................ 3

3.1 The Filling Process ..................................................... 33.1.1 Acid Density for Filling ..................................... 4

3.2 Fill-to-Form Processing .............................................. 4

3.3 Formation ................................................................... 43.3.1 Battery Preparation forFormation: Open Formation ..................................... 43.3.2 “Fill and Spill” Formation ................................. 53.3.3 Saturation/ Electrolysis Formation ................... 5

3.4 Formation Time .......................................................... 5

3.5 Completion of Formation ............................................ 6

3.6 Formation Algorithms ................................................. 6

3.7 Initiation of Current Flow............................................. 7

3.8 Constant Voltage Charging ........................................ 8

3.9 Constant Current Charging ........................................ 8

3.10 Taper Current Charging ........................................... 9

3.11 Pulse Current Charging .......................................... 10

3.12 Rests and Discharges ............................................ 11

3.13 Sample Formation Algorithms & Profiles ................ 123.13.1 A Simple Algorithm ...................................... 123.13.2 More Typical Charge/Rest/ Charge Algorithms ........................................ 12

3.14 Development of a SuitableFormation Algorithm ...................................................... 14

4. Temperature Limits for VRLA Jar Formation ................. 15

5. VRLA Battery Manufacture using Plate Formation ....... 16

6. Technical and Theoretical Background .......................... 176.1 The Formation Process Explained ........................... 17

6.2 Formation Processes and Ah Input .......................... 18

6.3 Key Differences BetweenFlooded and VRLA Batteries .......................................... 19

7. Jar Formation – Additional Information ....................... 207.1 Battery Preparation for Formation –Sealed Formation ........................................................... 20

7.1.1 Plate Curing and Carbonation ....................... 20

7.2 Acid Filling ............................................................... 20

7.3 Control of Formation Temperature ............................ 23

7.4 Completion of Formation .......................................... 25

7.5 Alternative Jar Formation Options ............................ 25

Table Of Contents

8. Battery Design ................................................................ 268.1 Plate Height/ Plate Spacing Ratio ............................ 26

8.2 Battery Case Draft ................................................... 26

8.3 Active Material Additives ......................................... 26

8.4 Electrolyte Additives ................................................ 27

9. Separator Optimization .................................................. 279.1 Volume Porosity ....................................................... 29

9.2 Saturation Level ....................................................... 29

9.3 Caliper ..................................................................... 29

9.4 Compression ........................................................... 29

9.5 Grammage ............................................................... 30

9.6 Surface Area ............................................................ 30

10. Separator Designs to Improve Wet Formation ............ 31

11. VRLA Gel Batteries ....................................................... 33

12. Formation Equipment and Layout ............................... 3412.1 Battery Connections .............................................. 34

12.2 Formation Bay or Circuit Configurations ................ 35

12.3 Critical Maintenance of Formation Equipment ....... 36

12.4 Power Quality and Equipment Costs ...................... 36

13. Battery Monitoring During Formation ......................... 3713.1 Electrical Monitoring .............................................. 37

13.2 Temperature Monitoring ......................................... 39

13.3 Gas Monitoring ...................................................... 39

14. Post-Formation Handling andIn-Line Product Testing ...................................................... 40

14.1 Visual Standards .................................................... 40

14.2 In-Line Product Testing .......................................... 4114.2.1 Open-Circuit Voltage Measurement ............. 4114.2.2 AC Impedance Measurements .................... 4214.2.3 High-Rate Discharge Measurements .......... 43

15. Troubleshooting: Problems and Solutions .................. 44

16. References .................................................................... 48

Appendix 1:Glossary of terms and abbreviations ..................................... 49

Paragraph Page Paragraph Page


Listing of Figures

Figure Page

Figure 1. Examples Of Techniques For TheInitiation Of Formation Charging ............................ 7

Figure 2. Examples Of Single-And Multi-StepCurrent-Limited Constant-VoltageFormation Profiles .................................................. 8

Figure 3. Examples Of Stepped Constant-CurrentAnd Conventional CC Formation ProfilesCompared To An Ideal Formation Curve. ............... 9

Figure 4. Examples Of The Progressive InfluenceOf Temperature Monitoring On TheEfficiency Of The Formation Process. .................. 10

Figure 5. Taper Current Charging. ...................................... 11

Figure 6. Examples Of Pulsed ChargingAlgorithms. .......................................................... 11

Figure 7. Typical Constant-Current FormationProfiles For A 12V/20Ah VRLA Battery. ................ 12

Figure 8. Typical Constant-Voltage AndTaper-Current Formation Profiles ForA 12V/20Ah Battery ............................................. 13

Figure 9. Typical Constant-Current FormationProfiles With Rests Or A DischargeFor A 12V/20Ah VRLA Battery. ............................. 14

Figure 10. The Filling Process Within A VacuumAnd Non-Vacuum Fill. .......................................... 21

Figure 11. Conceptual View Of the FillingProcess For A VLRA Cell. .................................... 21

Figure 12. Action On The Leading Edge Of TheLiquid In A VRLA Cell Filling Process. ................. 22

Figure 13. 2.5 Ah And 25Ah Spiral-WoundSingle-Cell Internal TemperaturesDuring Different Fill-To-Form Conditions. ............. 24

Figure 14. 6V/100 Ah Prismatic BatteryTemperature Data During Fill-To-FormTime With Different Conditions. ............................ 25

Figure 15. Solubility Of Lead Sulfate InSulfuric Acid At 25ºC. .......................................... 27

Figure 16. Mean Pore Size Vs. Kr BetSurface Area. ....................................................... 30

Figure 17. Impact Of Surface Area (m2/g) OnWater Wicking Height While Under20% Compression, After 24 Hours. ..................... 31

Figure 18. Effect Of Fiber Mix And SegregationOn Vertical Wicking Speed. ................................. 31

Figure 19. Upward And Downward WickingHeight For Oriented AndNon-Oriented Fibers. ........................................... 32

Figure 20. Battery Connections For SeriesStrings, Series-Parallel Arrays AndSeries-Parallel Matrixing. ..................................... 35

Figure 21. AC Ripple Voltage And CurrentRepresentation And Its Effect OnCell Temperature And Cycle Lifetime. .................. 37

Figure 22. Typical Self-Discharge CurvesFor VRLA Batteries. ............................................. 41

Figure 23. High-Rate Discharge Voltage/TimeCurves For Acceptable AndUnacceptable Battery PerformanceOn A 5-Second Test. ............................................ 43

Figure Page

Listing of Tables

Table Page

Table 1. Typical ampere-hour inputs in relationto wet paste weight and dry curedpaste weight. ....................................................... 19

Table 2. Typical AC Impedance Values For AVariety Of Thin-Plate VRLA Single CellsAnd Batteries Fully Charged At 25ºC. .................. 48

Table 3. Sample OCV Chart Used InManufacturing To Sort Cells Or BatteriesAfter Formation Or Recharge. ............................. 49

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The brochure is divided into several sections:

1. IntroductionThe purpose of this brochure is to guide the battery manufacturer in the formation ofVRLA (Valve Regulated Lead Acid) batteries. The information is nominally confined to“small” VRLA batteries with capacities in the range 1.2 Ah to 100 Ah. Because “jar”formation of VRLA batteries is far more difficult than plate formation, this aspect of VRLAbattery formation will comprise the largest section of the brochure.

■ Sections 2 through 5 deal with practical issues related to VRLA batteryformation, and deal mainly with jar formation.

■ Section 6 deals with the technical and theoretical background.

■ Section 7 gives additional information about jar formation.

■ Sections 8 through 10 give battery and separator design guidance.

■ Section 11 is a brief overview of VRLA gel batteries.

■ Sections 12 through 14 deal with formation equipment, battery monitoringand product testing.

■ Section 15 deals with troubleshooting formation problems.


2. Plate formation vs. jarformation for VRLA batteriesThe first decision the VRLA battery manufacturer has totake is whether to use a plate formation or jar formationprocess, and this section highlights some of the issuesthat need to be taken into account before making thisdecision.

Plate formation may result in fewer manufacturing andtechnical problems in respect of battery design, processcontrol, quality, performance and life. The merits of plateformation are particularly apparent for larger, highercapacity batteries where a long cycle life and/orcalendar life is required. However, particularly for thesmaller batteries being discussed in this brochure,many battery manufacturers are choosing jar formation.This may be for reasons of cost and convenience, butmay also be because the battery design does not lenditself well to plate formation. This may apply for examplewith thin plate cylindrical or prismatic battery designs.The decision as to which process to use will be dictatedby the detailed battery design and manufacturingconstraints as described in more detail later. However,there are other manufacturing and cost issues to beconsidered. The total cost of the plate formation/drycharge process may be higher than jar formation whenone takes into account the following factors:

■ The cost associated with the neutralizing andcleaning or disposing of the plate wash water.This water must be neutralized and cleaned ofheavy metals before it can be recycled ordischarged into a public sewer system.

■ The capital and operating cost of the dry chargeoperation (e.g. inert gas drying).

■ Post assembly charge and discharge cycles torecover the capacity loss that is inherent in thedry-charge process.

■ Plate lug cleaning before final assembly.

Practical issues related to VRLA battery and jar formation

2

The decision as to whether to plate form or jar form willbe based on a number of factors which the batterymanufacturer needs to take into account, and will bediscussed in more detail later. Some general guidance isgiven below:

Plate forPlate forPlate forPlate forPlate formation – should be used in the followingmation – should be used in the followingmation – should be used in the followingmation – should be used in the followingmation – should be used in the followingcircircircircircumstances:cumstances:cumstances:cumstances:cumstances:

■ Plates for tall batteries■ Plates for large, high capacity batteries■ Plates for very long life batteries■ Battery with high L/d ratio (>100)

(see section 10.1)

Jar forJar forJar forJar forJar formation – consider in the following cirmation – consider in the following cirmation – consider in the following cirmation – consider in the following cirmation – consider in the following circumstances:cumstances:cumstances:cumstances:cumstances:■ Cylindrical battery design■ Thin plate prismatic battery design■ Battery with low L/d ratio (<100) (see section 10.1)■ Large separator fringe area■ High separator grammage (>=2g/Ah)■ High surface area separator

Other issues, which also need to be considerOther issues, which also need to be considerOther issues, which also need to be considerOther issues, which also need to be considerOther issues, which also need to be considered for jared for jared for jared for jared for jarforforforforformation:mation:mation:mation:mation:

■ Whether single cells or monoblocs, and howmany cells in the monoblocs (e.g. 3 or 6 cells).This will have an impact on the efficiency ofcooling and temperature variations between cells.

■ If plates have been cured to produce high levelsof tetrabasic lead sulfate (4BS) the plates may bemore difficult to form, and require a higher chargeinput during formation than for tribasic lead sulfate(3BS) cured plates.

■ The inclusion of red lead in the positive paste mixwill assist jar formation and enable lower Ah inputand shorter formation times. It will also improvethe initial electrical performance.

In principle all VRLA batteries could use plates preparedusing plate formation/dry charge: but not all VRLAbatteries can be successfully jar-formed. The informationabove is given for guidance only, and the suitability of aparticular battery for jar formation should be establishedby careful experimentation.

Jar formation of VRLA batteries is actually quite acomplex process and will now be dealt with in detail.



3

3. The VRLA Formation Process –Jar Formation3.1 The filling processThe formation process for valve-regulated lead-acid(VRLA) cells and batteries really begins with the fillingprocess. Several approaches can be taken to filling,including:

■ Gravity top fill, single or multi-step■ Gravity bottom-up fill■ “Push” fill where electrolyte is pumped into the

cell or battery, usually from the bottom up (usableonly with spiral-wound products)

■ Soft-vacuum fill (>~20mm Hg), single or multi-step, possibly with a “push-pull” step to distributeelectrolyte more evenly

■ Hard-vacuum fill (<~10mm Hg)

The first, a gravity top fill, is the simplest approach thatcan be used for any cell or battery (hereafter referred to,collectively, as “batteries”) and just involves pouringelectrolyte into the headspace at a rate that the batterycan accommodate. It can be done slowly with a singleaddition or in several measured amounts. This is arelatively slow process but it has advantages in that heatis generated slowly, there is not likely to be damage tothe AGM separator and there is only a limited effect fromcarbon dioxide released from carbonated pastesurfaces. There is the possibility of incomplete wettingdue to trapped gas pockets. Heat generation in largerbatteries can be counteracted by chilling the electrolyte(typically to 0 to –10oC) and/or the unfilled elements and,if necessary, putting the filled battery into a chilled waterbath. The measures used depend in large part upon thesize of the battery. For small products (1.2-10Ah), simplebath cooling after fill is sufficient (and this may not evenbe necessary for very small products). For larger sizes(10-100Ah), chilled electrolyte and bath cooling may bemandatory. Fill times are of the order of 10-40 minutes.

Gravity bottom-up, or “dunk,” filling simply involvesdipping a cell or battery into a bath of electrolyte (thecase having a hole or holes in the bottom to allowingress of acid) until wicking has resulted in completefilling of the separator and plate pores. This is also aslow process (several minutes), and has the advantagesand drawbacks listed above for gravity top fill. An addeddisadvantage is that the filling hole has to be sealedbefore the battery goes into formation. In fact, simplyletting the battery take as much acid as it wants is very

reproducible in terms of fill weight and the finalsaturation level is typically ~95% (i.e., the plate stackdoesn’t saturate).

“Push” fill is a specialized technique for spiral-wound-type products where electrolyte is forced up through thewound element, either from the bottom or using a probein the wound-element mandrel space. This is faster thanthe gravity-fill techniques (around 30-60 seconds) and,thus, requires more care in thermal management.

Soft-vacuum filling involves drawing a moderate vacuumlevel and allowing the element to “suck in” electrolyte atits own rate. As this approach doesn’t usually result inuniform electrolyte distribution there is often a “push-pull” (pressure-vacuum) finishing step to physicallymove electrolyte around to help diffusion. The filling rateis moderate (30-60 seconds) so thermal management ismandatory, along the lines of that given above for thegravity-fill approach.

Hard-vacuum filling is a very rapid technique (on theorder of 1-10 seconds for sizes 1.2-25Ah) and is, thus,attractive for high-volume manufacturing. However, italso requires extreme care both during filling and forprocesses prior to filling. In addition to speed, hard-vacuum filling can result in uniform electrolytedistribution due to the almost total absence of airdisplacement. However, the absence of air also meansthat the paste is very reactive and the rapid introductionof electrolyte results in very high heat generation over ashort period of time. Thus, thermal management iscritical with this type of filling and it is impractical over asize of ~50Ah due to the inability to dissipate the heatrapidly generated, even with the chilling stepsmentioned above. Poor thermal management can resultin staining of the AGM separator by dislodged pasteand/or plate deformation and case bulging due to heatand, possibly, steam generated from the filling reaction.In this type of filling, the formation of hydration shorts(lead sulfate in the separator) is also possible due to thehigh temperatures and low acidity conditions that canbe generated. Plate carbonation during processing isalso a problem because the rapid introduction ofelectrolyte can result in a “burst” of liberated carbondioxide, which can help to defeat the vacuum createdand result in low fill weights. Further liberation of CO2

can cause regurgitation of electrolyte in extreme cases.Separator damage can also result from the hydraulicaction of the electrolyte if it is added too quickly, thuspromoting plate-to-plate shorting due to the removal ofoverlapping separator between adjacent plates.

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3.1.1 Acid Density for Filling3.1.1 Acid Density for Filling3.1.1 Acid Density for Filling3.1.1 Acid Density for Filling3.1.1 Acid Density for Filling

This will depend on the battery application, the desiredfinal density, and the amount of sulphation achievedduring paste mixing. A typical filling acid density wouldbe 1.26 with a final density of 1.28. Finished aciddensities are normally in the range 1.28 to 1.32,depending on the application. Standby batteries tend tohave lower densities (1.28) while high-rate batteries(aircraft, engine start) may have a higher density(~ 1.30). For deep cycle batteries the specified aciddensity may be in the range 1.28 – 1.32. With openformation the acid s.g. can be checked and adjustmentsmade if necessary. For sealed formation, calculationsneed to be accurate as it is not possible to correct theacid s.g. after formation. Some VRLA batterymanufacturers monitor the fill/ formation weight loss andthen add an equivalent amount of water or diluteelectrolyte before sealing the battery.

3.2 Fill-to-Form ProcessingThe time gap between electrolyte filling and initiation ofthe formation process is more important than may berealized. Even though VRLA batteries are electrolyte-deficient and there is more than twice the amount ofpastes as there is acid (on an ampere-hour basis), asignificant amount of acid remains unreacted if batteriesare put into formation immediately after filling. The longerthe delay between fill and form the more lead sulfate isformed. This facilitates the formation process, but it alsoincreases the resistance of the unformed plates(particularly the positive), as lead sulfate is an insulator.This is usually overcome by using 10% or more of redlead, Pb3O4, in the positive paste. Longer stand timesafter filling can also aggravate the conditions that caninitiate hydration shorts by allowing lead sulfate to slowlydissolve and diffuse into the separator. With a good fillingprocess this is not a problem, as even a mildly acidiccondition will suppress lead sulfate solubility, particularlyif sodium sulfate is used as an additive in the fillelectrolyte. However, in cases where fill conditionsresulting in areas of the plate stack where hot electrolytedepleted of acid can exist, batteries are put ontoformation as quickly as possible after fill. When this isdone, there is the danger of the battery overheating, asthe formation process generates heat, particularly earlywhen high plate resistances result in high I2 R heating,and additional heat is still being created by the ongoingfilling reaction (which is very exothermic).

In order to allow the filling reaction to go to completionand allow the battery to cool adequately, a fill-to-formtime of between 2 and 4 hours is recommended.

3.3 FormationThere are a number of factors to be considered inmatching the correct formation algorithm to a givenproduct, among these being:

■ Product sealed or open?■ Temperature control and the use of air or water■ Formation time■ Desired level of completion of formation

(i.e., % PbO2)■ Formation algorithm used (CC, CV, taper, pulse,

rests, discharges?)■ Battery connection series-strings only, series-

parallel strings or series-parallel matrix?■ Monitoring parameters during formation■ Critical maintenance of formation equipment■ Post-formation handling and product testing

3.3.1 Batter3.3.1 Batter3.3.1 Batter3.3.1 Batter3.3.1 Battery Pry Pry Pry Pry Preparation for Foreparation for Foreparation for Foreparation for Foreparation for Formation:mation:mation:mation:mation:Open ForOpen ForOpen ForOpen ForOpen Formationmationmationmationmation

For jar formation the easiest technique is “open”formation, which usually means a condition where thevent valve has not been put in place. (The alternative,less frequently used technique of sealed formation, isdiscussed in section 7.1). Open formation may alsoindicate a formation where the battery headspace isopen to the air. In either case, batteries are usuallyflooded, or close to it, and have the capability of removalor addition of acid during processing. Open formationsare useful in that plate processing is not as critical (interms of carbonation), heat dissipation due to gassing isgreater by about an order of magnitude than in sealedformations (because the battery is formed in the floodedstate) and adjustments in saturation levels are possibleat any time. There are several approaches to openformation for VRLA batteries, among them being:

■ Saturated or near-saturated condition withprovision for excess electrolyte handling;

■ So-called “fill-and-spill” formation, where batteriesare formed saturated and then the electrolytelevel is adjusted at the end of formation; a variantof this is two-step formation, where the battery isfirst formed with dilute electrolyte which isreplaced after formation with a higher specificgravity acid closer to the desired operationallevel;

■ Saturated or near-saturated formation open,followed by saturation and electrolysis to achievea target saturation level, usually ~95%.



3.3.2 “Fill and Spill” For3.3.2 “Fill and Spill” For3.3.2 “Fill and Spill” For3.3.2 “Fill and Spill” For3.3.2 “Fill and Spill” Formationmationmationmationmation

This formation approach involves formation in a floodedstate, followed by simple pouring off of excesselectrolyte. This results in a near-saturated conditionfollowing formation (trapped gas in the plate poresensures that some electrolyte is absorbed and, thus,there is a small amount of void space in the formedbattery), which may result in higher-than-usualovercharge gassing and weight losses early in life and,possibly, acid leakage during heavy overcharge. Thisapproach has been promoted by H&V for use with theirHovosorb II organic fiber/glass separator [1] (see alsosection 10) and is particularly well suited tomanufacturing processes with high manual labor inputsand those where precise control over finished batteryquality is not required. The saturation levels in the cellsare not precisely known and significant cell-to-cellvariations could exist. Heavy hydrogen gassing duringformation must be accounted for, but the high levels ofgas generation help with heat dissipation.

In principle, a two-step formation could be used forVRLA products as is done for flooded lead-acidbatteries. Here, the battery is filled with a relatively diluteelectrolyte for the initial formation process, after whichthe forming acid is dumped and the battery is refilledwith an electrolyte close to the desired final specificgravity after a finishing charge. The major problem forVRLA batteries is that the AGM separator (unlike floodedlead-acid separators) holds most of its electrolyte andany manipulation of the formed battery is likely to resultin separator damage.

3.3.3 Saturation/Electr3.3.3 Saturation/Electr3.3.3 Saturation/Electr3.3.3 Saturation/Electr3.3.3 Saturation/Electrolysis Forolysis Forolysis Forolysis Forolysis Formationmationmationmationmation

In order to have an accurately known saturation level inthe region of 95% after formation, a method has beendeveloped where a standard open formation is carriedout, followed by over-saturation and pouring off ofexcess electrolyte (much like “fill and spill” above). Thefully-saturated, formed battery (still open) is thensubjected to a period of electrolysis at a known currentlevel to drive off an accurately-known amount of water,thus getting the battery to the desired saturationpercentage, after which completion of battery assemblycan be carried out.

3.4 Formation TimeVery early work done by Ritchie at Eagle-Picher showedthat flooded lead-acid batteries could be formed in ~2weeks to a very high PbO2 level with minimal weight lossand consumption of just over the theoretical ampere-hour input of 241 Ah/kg of PbO. This is not feasible inlarge-scale manufacturing, but it does set a baselineagainst which more practical formation algorithms andtimes can be measured. Suggestions for typical ampere-hour inputs in relation to wet paste weights are given insection 6.2. In practice, small VRLA batteries are formedwithin 24-48 hours. The actual formation time will bedependent on a number of factors, but a general rule ofthumb is that cell/battery capacities of ~20Ah or lessrequire a roughly 24-hour formation, while larger sizesup to 100Ah can normally be formed in ~48 hours.Smaller batteries are easier to form because they aremore compact and voltage drops across the plates areless. They also tend to have better heat-dissipationproperties and can be formed at higher currents.

Formation time is not the only criterion. Heat buildup isan issue that will tend toward longer formation times.High PbO2 levels move the time in the same direction,as does the requirement for lower formation weightlosses. The positive plate (PbO2 level) is the keyindicator of the completeness of formation (see alsosection 7.4). In fact, the negative active material, orNAM, forms relatively easily and it is rare that formationof the NAM is the limiting factor. If manufacturingthroughput were not an issue, all formations would bedone over several days, as most benefits flow from longformation times. However, formation throughput is ofparamount importance and so the goal is almost alwaysto achieve complete formation in a minimum amount oftime. In order to accomplish this in large-scalemanufacturing, it is important to have a deeperunderstanding of the chemistry of the formation process,and more detail is given in section 6.1. The chemistryinvolved in formation is fairly complex, consisting notonly of the basic chemistry of conversion of lead sulfateto sponge lead and lead sulfate, coupled with theovercharge processes involving the decomposition ofwater, but also more subtle issues such as electrolytediffusion and gas bubble formation.



3.5 Completion of formationOne or more of the following parameters can bemeasured to determine whether formation is complete:

■ Battery, cell and individual electrode potentialsbecome high and constant. Electrode potentialsare determined using either cadmium wire ormercury/mercurous sulfate reference electrodeson test batteries.

■ Top-of-charge voltages (TOCV) become constant,but will vary for individual VRLA batteries,depending upon the amount of oxygenrecombination occurring at the end of formation;the more oxygen reduction taking place the lowerthe TOCV. This will be influenced by whethersealed or open formation is used. In fact, if agiven formation system monitors TOCV valuesthese can be used for matching small batteriesinto larger units, as this is a critical performanceparameter.

■ At the same time, electrolyte specific gravitybecomes constant at some high level (relative tothe starting density) due to conversion of sulfatein the unformed plates to sulfuric acid.

■ Both plates gas uniformly and strongly.■ Temperature rises steeply toward the end of

formation at a given applied current, reachingvalues as high as 65-75oC if the finishing currentis not reduced.

■ Internal examination of a cell or battery wouldshow that the plates are uniformly colored and arewithout white spots (unformed lead sulfate); thenegatives are soft with a gray metallic sheen andthe positives are hard and are dark brown toblack in color.

In practice, most of these parameters cannot bemeasured routinely, particularly in a large matrix ofbatteries in a formation bay. With a given VRLA product,the normal approach is to carry out test formationalgorithms on a few batteries, which are monitored andthen autopsied in order to determine if they meet theabove criteria. Following the establishment of aproduction-worthy formation algorithm, all batteries arethen manufactured using it, with some form of periodicsampling and testing to ensure the desired level ofquality and uniformity.

Additional information is given in section 7.4

3.6 Formation AlgorithmsThe best algorithms to use in forming VRLA batteriesdepend upon a number of factors, ranging from capitalinvestment to desired product quality and the intendedapplication. The battery manufacturer will need to carryout tests to establish the best algorithm for his specificmanufacturing process and battery application, but thefollowing guidelines may be useful.

The optimum algorithm is likely to include a numberof steps:

■ Low initial current to minimize temperature rise atthe start of formation. There may be acontinuation of the heat production from theoxide/acid filling reaction. There may also be avariable fill-to form hold time due to the time lag infilling a formation circuit queue. The low initialcurrent will compensate for possible high batteryresistances. The low current charge should becontinued until the battery temperatures havefallen below 50°C.

■ One or more steps at a higher current during themain part of the formation process while batteryresistance is at its lowest and heat generation isat a minimum.

■ One or more steps at a lower current as thegassing phase is reached towards the end offormation.

■ The formation process may also include restperiod(s) and/ or discharge step(s).

The chosen charging approach will usually depend onthe desired amount of capital investment and/ orexperience from making flooded lead acid products.The possible choices are:

■ Constant-voltage (CV)■ Constant-current (CC)■ Taper-current (TC)■ Pulsed-current (PC)

When making the choice of appropriate chargingequipment, it should be noted that the chargingequipment from Digatron/ Firing Circuits Inc., offerscomputer control with optional battery monitoring toprovide optimum control of charging parameters.

More information about each of these processes isgiven on the next page.



Examples Of Techniques For The InitiationOf Formation Charging

Current,amperes

A. Low-current initiation

Current,amperes

Current,amperes

Formation time, hours

B. Ramp-current initiation



C. Abrupt or high-current initiation

Figure 13.7 Initiation of Formation Current FlowBefore formation current flow is initiated, mostmanufacturing operating procedures include so-called“continuity checks,” where individual battery strings arechecked with an ohmmeter to ensure that the resistanceof the string, while very high, is not infinite (indicating abattery with an open connection (poor COS or squeezeweld) or a defective formation connector lead-to-terminalcontact). If an abnormally high or infinite resistancereading is taken, the formation room personnel mustidentify the source of the problem; otherwise, a completestring of batteries will not be formed and, in a series-parallel array, the other strings will receive too-highcurrent levels.

Initiating current flow can be difficult if the plates areheavily sulfated and/or the fill-to-form time has beenlong, thus depleting most of the sulfuric acid in theelectrolyte and raising the liquid resistivity. The use ofred lead in the positive paste, carbon in the negativepaste, as well as sodium sulfate in the fill electrolyte willhelp to minimize the high initial resistance.

If a high-inrush current level is applied when the initialbattery resistance is high, the voltage will be driven tohigh values and most or all of the current will go intoheat generation and gassing. After a period of timethese processes will diminish and conversion of leadsulfate to the active materials will take over and theformation will proceed in a normal fashion. However, ashort initiation charge period of 0.5 to one hour at lowcurrents can be applied in order to generate some acidand improve the conductivity in the plates, or the currentcan be ramped up slowly over an hour or so, as shownin Figur Figur Figur Figur Figure 1e 1e 1e 1e 1, before the main formation current is applied.

Initial resistance to proper current flow can be detectedeither by an immediate rise in charge voltage to veryhigh levels (or to the voltage limit if constant-voltagecharging is used) or by a relatively sharp temperatureincrease. Unless the battery plates are very heavilysulfated, after a short period the voltage andtemperature will drop to normal levels, which aretemperatures below ~50oC and voltages of ~1.8-1.9volts per cell. There will then be gradual rises in bothtemperature and voltage, but because almost all of theformation current is going into lead sulfate conversionthese increases will be very gradual.



3.8 Constant-Voltage ChargingCurrent-limited constant-voltage (CV) charging iscommonly used for cyclic charging of VRLA batteries,but its utility in formation is more limited, largely due tocost and its effect on product uniformity. Precise voltage-control limits are expensive in terms of formationelectronics and in forming VRLA batteries they are notnecessary. The primary drawback is that, as in CVrecharge, the current taper toward the end of formationresults in relatively long charge times. In order tominimize this and speed up formation times, multi-stepCV algorithms can be used, by programming for current-limit reductions when the voltage limit is reached. Thisthen becomes a stepped constant-current formation, butwith a voltage limit (usually ~16V for a 12V battery) tominimize gassing and grid corrosion. Typical examplesof single-step CV and stepped-CV/CC algorithms areshown in FigurFigurFigurFigurFigure 2.e 2.e 2.e 2.e 2. The last step usually allows for acurrent taper when the voltage limit is reached, theduration depending upon the desired formation time.

There are a number of advantages and drawbacks toCV charging. On the plus side, overcharge is minimizeddue to the current taper during the finish of formationand so the charge efficiency is relatively high andconcerns about gas monitoring and ventilation are lessimportant. Balanced against this (in addition to cost) area number of drawbacks:

■ With a significant time in the current-taper mode,the total Ah input must be integrated electronically(rather than simply timed as with CC formation).

■ In single-step CV, the long charge “tail” lengthensformation time significantly.

■ Because voltage is applied to long strings orseries-parallel arrays as a multiple of a givenvolts-per-cell, actual charge voltages for each cellcan be highly variable. More seriously, paralleledstrings can draw different currents based upontheir cumulative DC resistances; this can have theeffect of routing high currents through individualstrings early in formation, which can result in largeimbalances of total ampere-hours passed throughdifferent strings. In the extreme, this can result instrings with low initial DC resistance going intothermal runaway, particularly for large batterieswith poor heat-dissipation capabilities.

■ If strict voltage control is desired, temperature-compensated charging must be used, whichfurther increases cost. Temperature issues can beminimized by using lower charge voltages, butthis will increase formation times significantly.

Voltage/Current

Formation time

A.Single-Step Current-Limited Constant-VoltageFormation Profile

Voltage/Current

Formation time

B.Multi-Step Current-Limited Constant-VoltageFormation Profile

Examples Of Single- And Multi-Step Current-LimitedConstant-Voltage Formation Profiles

Figure 2

= Formation Charge Current= Formation Charge Voltage

3.9 Constant-Current ChargingIn CC charging, voltage control is not required (althoughthere is always a voltage limit such as 2.80 volts per cell)and this reduces the cost of the charging equipment.Using single-step or two-step formations at high currentscan also reduce formation times, but this results in lowercharge efficiencies and large amounts of overchargeand gassing. The most common approach is to use asingle-step CC algorithm, possibly with one or more restperiods (see below) or discharges. This is not efficient,since at low currents overcharge is minimized but totalformation time is long whereas with high currents theforming time is shortened but the overall chargeefficiency is reduced. More innovative, multi-stepalgorithms are now in use where relatively high currentsare used early in formation and lower finishing currentsare then applied, either as a two-step or multi-stepalgorithm. Dramatic gains in charging efficiency can berealized, as shown conceptually in FigurFigurFigurFigurFigure 3 [2].e 3 [2].e 3 [2].e 3 [2].e 3 [2]. In somecases this is done as a fixed, programmed algorithmwith defined current levels for pre-set time intervals.Other approaches involve monitoring of battery



Examples Of Stepped Constant-Current AndConventional CC Formation Profiles Compared ToAn Ideal Formation Curve.Note The Disparity In Overcharge Amounts

Figure 3

Stepped Constant-Current

Conventional CC Formation

I

t

I

t

Ideal current curve

Several-step current curve

Ideal current curve

Several-step current curve

Current curve of several-step formation

Current curve of conventional formation

parameters in order to apply optimal current levels foras long as possible. One example of this is shown inFigurFigurFigurFigurFigure 4 [3]e 4 [3]e 4 [3]e 4 [3]e 4 [3], where battery temperature is used as thecontrol variable. As can be seen, this allows for an initialhigh CC level, followed by step-downs to lower currentsbased upon battery temperatures.

The major advantages of CC charging are that it iseasily programmable, it is relatively rapid and the totalampere-hour input can be determined easily. In addition,the current level is controlled, so even in series-parallelarrays battery damage due to high charge currents asnoted above for CV formation is largely avoided.However, several drawbacks also apply:

■ Single-step CC formation is either very lengthy(low current) or very overcharge-intensive (highcurrent).

■ Heavy overcharge results in high heat production,grid corrosion and gassing.

■ Voltage regulation on charge is not possible,except for the high upper limits used (2.8-3.0 V/cell or more)

On balance, this is the simplest approach to formationand is the most commonly used, particularly in multi-step algorithms. As programmable controllers forformation systems are now commonly available andinexpensive these approaches, though seeminglycomplex as shown in FigurFigurFigurFigurFigure 4e 4e 4e 4e 4, are very straightforward.They are also a more tolerant approach when poorlyregulated input (i.e., “dirty”) power and/or inexpensiveformation electronics are used.

3.10 Taper-Current ChargingTaper-current (TC) charging for formation combinessome of the best aspects of CV and CC approachesand is probably the least expensive of the three. As it isnot a common approach, FigurFigurFigurFigurFigure 5 e 5 e 5 e 5 e 5 shows a typical circuitfor TC charging, along with a typical charging curve.This is really the simplest of circuits. A power supply iswired in series with a load resistor and a battery string orstrings to be formed. If desired, some form of sensing ofbattery parameters (voltage, temperature, etc.) can beincluded to provide feedback control. When formation isinitiated, current flows according to the rating of the loadresistor and the voltage difference between the powersupply setting (typically a high value of 2.6-2.8 V/cell)and the battery array (which will initially have a very lowvoltage). At the beginning of formation, the voltagedifference is great, on the order of ~1V/cell, and theinrush current is relatively high, as in CV charging. Asthe cumulative battery array voltage climbs the

formation current decreases because of the decreasingvoltage difference with the power-supply setting. UnlikeCC charging, when the battery array voltages climb intothe gassing region the charge current is tapering off.However, the current does not taper off as sharply aswith CV charging because of the higher voltage setting.Moreover, if the TOCV is low for the formation array dueto an unusually high oxygen-recombination current drawthe current at the end of formation will increase due tothe widening gap between the power supply voltage,which is fixed, and the decreasing end-of-chargevoltage. Initial and final currents are roughly set bychoices of power-supply settings and resistor values.These yield an approximate formation voltage/timeprofile, but the exact shape of the curve will varyconsiderably depending upon the charge-acceptanceproperties of the battery array being formed. This can beviewed as both a strength and a weakness of this


A.Normal formation. The batteries are placed in anon-flowing water pool.

B.Formation in flowing coolant, with maximum initial current.Limit set on voltage but not on temperature.

C.Formation with initial maximum current limit,followed by temperature and voltage limits.

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Examples Of The Progressive Influence Of TemperatureMonitoring On The Efficiency Of The Formation Process.

Figure 4

= Current= Voltage= Battery Temperature= Coolant Temperature


approach. It is well suited to VRLA formations, as manyproducts do not require precise voltage control. Insummary, TC charging has the following advantages:

■ Capital input for formation charging equipment islow if inexpensive power supplies are used;however, poorly regulated supplies can not onlytransmit, but also at times amplify, line fluctuationsto the charging system.

■ It allows for a relatively fast formation with onlymoderate overcharge amounts by allowing highinrush currents (relative to CC) as well as highfinishing currents (relative to CV).

■ To some extent, the formation profile is variableaccording to the charge-acceptancecharacteristics of the battery array being formed.

There are also a number of drawbacks, as follows:■ Because the current tapers, Ah input must be

determined by electronic integration.■ The amount of overcharge is high relative to CV or

multi-step CC charging.■ Voltage and current are not controlled, so the

uniformity of formation profiles for different batterylots is not high; total Ah input may varysignificantly with product uniformity going intoformation.

■ The use of unregulated power supplies can resultin shortened lifetimes in service.

3.11 Pulsed-Current ChargingPulsed-charge algorithms can be applied to theformation of VRLA batteries just as it is used in charge/discharge service; typical algorithms are shown inFigurFigurFigurFigurFigure 6e 6e 6e 6e 6. As can be seen, profiles analogous to CV orTC charging as well as pulsed CC can be used. Notethat in the “off” periods, rests or partial or completedischarges can be applied. The discharges are thoughtto be beneficial in eliminating surface charges from theplates, which can result in lower gassing levels; it hasnot been unequivocally established if this is, indeed thecase. A good deal of work has been done on usingpulsed methods, but it remains unclear whether productquality gains can be realized with this approach. Thereare clear advantages in enhanced heat dissipation whileallowing the use of relatively high currents (even late information) and in reduced gassing due to the reductionsin coulombic input per pulse as the gassing region isapproached late in formation. While most batterycompanies have investigated this for the above reasons,it is not commonly used.


In all cases, the coulombic input decreases as the top-of-charge is approached.

Time Time–

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+

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+

Constant Period, Decreasing Amplitude■ Pulse/Rest■ Pulse/Discharge■ Pulse/Discharge/Rest

Constant Amplitude, Decreasing Period

Examples Of Pulsed Charging Algorithms.

Figure 6

Taper Current Charging.

Figure 5

Typical TC Circuit

Typical TC Current/Voltage/Ah Curves

Charge current ( I ) =Power Supply Voltage - Cell Voltage (V)

Load Resistor (RTaper)

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3.12 Rests and DischargesOne of the major electrochemical problems in using anyof the above approaches in a continuous way (with theexception of pulsed charging) is that gas generation canseverely impede the efficiency of the formation processby retarding the diffusion of acid and water within the

plate pores. The charge efficiency of the positiveelectrode is relatively low even when completely formed,but in formation itself it is so poor that gassing of oxygencan begin after only a few hours, or even less. Later, thenegative plate will also begin gassing and in both casesthis hampers proper conversion of unreacted leadoxides deep in the plates to lead sulfate and thensubsequent reaction of the sulfate to the activematerials. The first step requires acid generated at theplate surfaces early in formation to penetrate into theplate interiors and the second reaction requires water toproduce sponge lead and PbO2. When either or both ofthe plates goes into gassing, this will force liquids out ofthe plate pores and into the glass-mat separator;eventually, with heavy gassing much of the electrolytewill be forced into the head space or even out of thebattery as regurgitated acid or acid spray.

These conditions are easily avoided by inserting one ormore rest periods or discharges into the formationalgorithm. In both cases, when the charge voltage isremoved gassing ceases and time is allowed for waterand acid to diffuse into the plate interiors. This allows forreaction of acid with any PbO remaining after filling andfill-to-form. When formation is reinitiated more leadsulfate has been generated and water is present as apart of the filling reaction. When formation is continuousgassing seriously impedes these processes. Thus, useof significant “off” times can actually result in faster, morecomplete formation processes. Rests or discharges canbe put in at fixed points in formation or they can beinitiated when a “trigger” voltage is reached. Theseconsiderations probably apply more to thicker-plate



A.Voltage, Temperature and Gassing Curves fora One-Step CC Formation

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Formation Time, Hours0 4 8 12 16 20 24 28 32 36

2

B.Same Curves for a High-Inrush Two-StepCC Formation Algorithm

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2

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Typical Constant-Current Formation ProfilesFor A 12V/20Ah VRLA Battery.

Figure 7

= Formation Current= Voltage= Temperature= Gassing Rate

products (2.0 mm or more) than those with thin plates(where diffusion paths are shorter and plate wetting ismore efficient due to the higher surface areas).

Which approach is better? Discharges are clearly morecomplex in terms of capital equipment and they willlengthen formation time relative to rests due to therequirement for replacing charge taken out during thedischarge. Discharges are thought to be beneficialbecause, in principle, they should increase theporosities of the plates and further aid acid and waterpenetration, as well as improve post-formationdischarge capacities. Little documentation is availablecomparing the effects of rest periods and discharges,so the technologist is left to weigh the possible benefitsgiven above against the significantly higher costs ofdischarge equipment. Both are clearly beneficial inreducing formation weight losses and in improvingfinished-product quality. For VRLA batteries requiringhigh post-formation PbO2 levels (90% or greater) andlong shelf lives (low residual PbO levels in the formedpositive plates) the use of one or the other is almostmandatory.

3.13 Sample Formation Algorithms & Profiles3.13.1 A Simple Algorithm3.13.1 A Simple Algorithm3.13.1 A Simple Algorithm3.13.1 A Simple Algorithm3.13.1 A Simple Algorithm

Sample formation profiles will now be considered thatmight be recommended for a typical 12V/20Ah VRLAproduct. The simplest approach would be a single-stage CC formation over, for example, 36 hours with atotal Ah input of four times the rated capacity, or 80Ah.Over a 36-hour period this would be a CC level of~2.2A, as shown in FigurFigurFigurFigurFigure 7a.e 7a.e 7a.e 7a.e 7a. This approach results inrelatively high temperatures toward the end offormation and large overcharge amounts and gassinglevels, but it will form the battery successfully. The porestructure may not be optimal due to the low initialcurrent and so a modification of this would be to use atwo-step CC algorithm with, say, 2 hours at 8A (16Ah)followed by 34 hours at 1.88A. (Figur(Figur(Figur(Figur(Figure 7b). e 7b). e 7b). e 7b). e 7b). For a CVformation, somewhat more time may be required or ahigh inrush current may be needed, accepting asomewhat lower charge input at 36 hours, as shown inFigurFigurFigurFigurFigure 8a.e 8a.e 8a.e 8a.e 8a. In order to increase the charge input towardthe end of formation a taper-charge algorithm may beused, as shown in FigurFigurFigurFigurFigure 8b. e 8b. e 8b. e 8b. e 8b. This has a high inrushcurrent as with CV but the current only tapers to ~30%of its initial value. This results in a higher Ah input, butalso higher temperatures and more gassing (weightloss) in the final 12 hours or so.

3.13.2 Mor3.13.2 Mor3.13.2 Mor3.13.2 Mor3.13.2 More Te Te Te Te Typical Charge/Rest/Charge Algorithmsypical Charge/Rest/Charge Algorithmsypical Charge/Rest/Charge Algorithmsypical Charge/Rest/Charge Algorithmsypical Charge/Rest/Charge Algorithms

An intermediate level of complexity can be appliedwithout going to the type of feedback approach used inFigurFigurFigurFigurFigure 3e 3e 3e 3e 3 (which is certainly acceptable). In this “typical”case, two rest periods are introduced into the 36-hourformation with the focus on CC charging. The restperiods can be shifted toward the end of formation asthere is, initially, a great deal of lead sulfate from thefilling process and it will take some time to consume thismaterial. (Given the current level imposed and theamount of lead sulfate expected to be present, a roughtime period can be calculated to where significant



Typical Constant-Voltage And Taper-Current FormationProfiles for a 12V/20Ah VRLA Battery

Figure 8

= Current= Voltage= Temperature= Gassing Rate

32..........48

A.Voltage, Temperature and Gassing Curves fora One-Step CV Formation

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Formation Time, Hours0 4 8 12 16 20 24 28

B.Same Curves for a One-Step Taper-CurrentFormation Algorithm

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gassing will begin; alternatively, voltage can bemonitored, as shown here, and “trigger” levels used tostart the two rest periods). Four hours total have beenallocated for rest periods; this could be put into one ortwo rests; but it makes more sense to use two. More restperiods and longer total rest times may also be suitablefor some VRLA thick-plate products.

In order to have a relatively fine pore structure in thepositive active material, a short, high-inrush currentperiod has been used to provide smaller, morenumerous PbO2 seed crystals upon which to build

during the rest of the formation. After this, a fixed CClevel can be used in combination with the two restperiods, as shown in FigurFigurFigurFigurFigure 9a.e 9a.e 9a.e 9a.e 9a. The rest periods arebeneficial not only in providing time for electrolytepenetration but also for keeping the temperature downcompared to a continuous one- or two-step CCalgorithm. Because the time spent in overcharge andresultant gassing is lower overall with rest periods(even though the charging current is higher tocompensate for the 4-hour off time), weight losses arealso reduced somewhat.

If a discharge were to be used instead of the two restperiods, it would be most beneficial to have it near theend of the formation, as shown in FigurFigurFigurFigurFigure 9b.e 9b.e 9b.e 9b.e 9b. As can beseen, only a partial discharge is carried out; acomplete discharge would obviously be more effectivein promoting pore formation and electrolytepenetration, but it would also require substantially moretime for the full discharge and subsequent recharge. Ifthis were done within the 36-hour schedule time itwould require much higher charge current levels but itcould be done. However, as noted, there is no clearevidence indicating that a discharge is more effectivethan rest periods. One advantage for a discharge isthat it could be used as a matching tool for buildingbattery modules into high-voltage packages, usingdischarge capacity and top-of-recharge data recordedduring formation. This would, of course, require that allbatteries be monitored and that the data be collectedand processed. The major cost, however, would be forequipment to carry out the discharges; in addition, ifthe formation time were extended this would reducethe battery throughput level somewhat and wouldrequire more formation stations to process the samenumber of batteries. However, finished battery qualityand uniformity would be improved significantly.

These are just a few examples of formation algorithmsthat might be employed for the processing of VRLAbatteries. The great flexibility in choosing anappropriate algorithm also introduces an equivalentamount of uncertainty. It is recommended that for agiven VRLA product significant R&D work be put intothe definition of suitable formation conditions. Whileeach company has its own approaches, the followingis a recommended procedure that should work for themajority of companies.



Typical Constant-Current Formation Profiles With RestsOr A Discharge For A 12V/20Ah VRLA Battery.

Figure 9

A.Current and Voltage Curves for a CC/RestFormation Algorithm

B.Same Curves for a CC/Discharge/RechargeFormation Algorithm


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3.14 Development of a Suitable FormationAlgorithmIt is assumed that a 6V/100Ah VRLA battery is beingdeveloped for Telecom use and it is necessary to findout how to form the product most effectively. Theoptimized formation algorithm will depend largely uponthe desired formation time, the design of the battery andthe user requirements. Without going into such details,the following steps can be used to define a suitablealgorithm.

■ Take at least 12 filled modules and monitortemperature between fill and formation; note thebattery temperatures at the initiation of formation.

■ Weigh the batteries prior to formation, but at theend of the fill-to-form period. Don’t assume thatthe electrolyte fill weight can be added to the pre-fill battery weight in order to get the pre-formationweight; all batteries, especially large ones that areprocessed open to the atmosphere (i.e., withoutthe top and vent valve in place), will lose weightbetween filling and formation due to evaporationand, in some cases, acid spraying orregurgitation. The primary loss is fromevaporation, which can be several percent of thetotal fill weight.

■ To as great a degree as possible, batteries shouldbe configured as they will be in a formation bay inmanufacturing. Formation of single units or a fewin series when they will be in large series-parallelarrays in production will not give an accurate ideaof the effectiveness of the formation process. Inaddition, thermal conditions should be close tothose that will be seen by the batteries inmanufacturing. Initial studies can be done withforming of small numbers of batteries, but itshould not be assumed that product quality wouldbe the same as in full-scale manufacturing.

■ Wire up the test batteries so that the followingparameters can be monitored: voltage, time,current (also with integration if CV or TC chargingis used, but also for CC to ensure that the correctAh input is applied) and internal pressure (ifbatteries are formed sealed). Reference-electrodemeasurements should also be taken and at somepoint several batteries should be formed with gascollection and analysis being done.

■ In order to get an idea of the capabilities of thebattery design for formation, an initial run shouldbe done using a very simple one-step CC, CVand/or TC charge, just to see how the batteryreacts to these “baseline” conditions. Then,several preferred algorithms should be applied,covering a range of times and currents, using restperiods and, possibly, discharges (even if this isnot to be done in manufacturing due to cost).



■ After formation, batteries should be weighed andcarefully inspected for cosmetic and productdefects (acid spray or leakage at lid/box seals orterminal posts, label damage, etc.). Teardownsshould be carried out to look at the plates in detail(visual inspection for white sulfate, color, hardness(PAM) or softness (NAM), distortion, massivecorrosion or growth). The separator should beinspected for holes/tears, damage from filling,staining by expander or paste and the possiblepresence of lead sulfate (hydration shorts). Thelatter can be determined using a sodium iodidesolution sprayed on the separator; insoluble leaddioxide shows up as a bright yellow precipitate.Electrolyte should also be squeezed out of theseparator at several points to determine specificgravity levels.

■ Negative plates should be dried and prepared forSEM, BET and porosimetry analysis; other testsmay also be carried out. Positive active materialshould be treated similarly. In addition, severalpositive plates should be stripped of activematerial and the grids should be inspected andweighed for general or localized corrosion duringformation. Wet-chemical analysis of the NAM (freelead, sulfate) and PAM (PbO2, sulfate, unformedPbO) should also be done. XRD should beapplied, if available, to define the amounts ofalpha- and beta-PbO2 generated at differentlocations on the positive plate surfaces.

■ Taking all of the data above, several iterations offormation algorithms should be applied to ensurethat the most effective algorithm has beendeveloped.

■ As a final step, a pre-production run should becarried out under actual manufacturing conditionsto ensure that the development work done on alimited number of batteries (particularly thethermal conditions and the series-parallelconfigurations) is relevant to full-scale production.

■ In addition to the above analytical work, fullelectrochemical characterization of the formedbatteries should be done to ensure that nominalquality levels and the desired uniformity havebeen achieved using the selected formationalgorithm. Self-discharge (shelf life)measurements should also be done to ensure thatthe degree of formation of the positive plate andremaining unformed oxide amounts areacceptable.

4. Temperature Limits For VRLAJar FormationFor jar formation of conventional flooded batteries, amaximum formation temperature of up to 65°C maybe permitted with no apparent harmful effect on thebattery performance: this is certainly the case for SLIbattery designs. Industrial battery designs may havesignificantly longer formation times and lowerrecommended maximum formation temperatures(e.g. 50°C).

The temperature during all stages of the filling andformation process is much more critical for VRLA jarformation. The control of temperature is necessaryfrom the initiation of formation until its completion.Sometimes it involves active control and at other timesit dictates passive processing conditions. The latter istrue going into formation, where the battery has beenfilled with electrolyte and allowed to stand for sometime before being placed in the formation environment.

With VRLA batteries, high formation temperatures mayresult in the formation of lead dendrites and/ orhydration shorts. Therefore the maximum formationtemperature should be kept below 40°C: and normallythis will require water cooling or forced air-cooling. Theformation regime may also include brief rest periods.Some VRLA battery manufacturers may specify amaximum temperature of 50°C or even 60°C, but thereare risks associated with this approach. In comparingformation at 60°C with formation at 40°C, it has beenfound that the PbO2 content is higher at 60°C, and thea/b PbO2 ratio is lower. However, the highertemperature has an adverse effect on the negativeplates, resulting in a decrease in battery capacity athigh discharge rates. The surface area of the negativeplates is decreased if formation is carried out at hightemperature, possibly because of deterioration of thenegative plate expander [4]. It is important to note thatif the measured temperature at the top of the cell is60°C, the maximum internal temperature inside the cellmay be significantly higher, 70°C or even as high as80°C. This has implications in respect of the stability ofthe negative plate expander, and it has been foundthat the surface area of the negative plates issignificantly reduced. Localized overheating may alsoresult in grid corrosion and/ or increased risk of leaddendrite formation.



In practice, sufficient time must be allowed after fillingand before the start of formation to allow the heatgenerated during the filling process to have passed itspeak. The thermal management during the fillingprocess should not be too efficient or the exothermicacid-oxide reaction may “shut down” if the battery is toocold, and start up again – generating excessive heat –when the formation process is started. The degree ofcooling (or even heating) during formation needs to berelated to a number of factors including:

■ Product size■ Temperature at start of formation■ Cooling technique■ Plant temperature■ Sealed or open formation

Additional information is given in section 7.3.

5. VRLA battery manufactureusing PLATE FORMATIONIn plate formation the pasted and cured positive andnegative plates are placed in bottomless slotted crateswith relatively wide spacing so that no separator isneeded. The positive and negative plates are placedalternately so that the lugs of all the positive plates areon one side of the crate, and all the negative plate lugsare on the other side of the crate. “Tacked” or “tackless”formation can be used. With “tacked” formation leadbars are tacked onto the lugs joining all the positiveplates together, and all the negative plates together, toform a 2v cell. In “tackless” or “burnless” formation, theplate lugs make contact with lead bars wedgedbetween the walls of the crate and the plate lugs: aspecial clamp ensures close contact between the platelugs and the lead bar. Or the plate lugs make contactwith lead bars at the bottom of the crate. The crates areimmersed in dilute sulfuric acid (e.g. 1.100 s.g.) and aformation charge passed through the crates: a steppedcurrent may be used to maximize formation efficiency.Because the sulfuric acid is present in excess, there israrely any problem with excessive formationtemperatures. After formation, the plates are washedand dried to produce dry charged plates. (Oxygenneeds to be excluded during the drying of the negativeplates). This stage of the process is exactly the same forVRLA batteries as it is for conventional flooded batteries.The formation regime, total Ah input, and dry chargeprocess can be exactly the same as for conventionalflooded batteries.

A critical issue with plate formation is to ensure that theplates do not “bow” during formation. This is a particularconcern with positive plates if they have been overpasted on one side. A high current density should alsobe avoided. If the plates are bowed, the plate grouppressure will be non-uniform when the plate group isassembled which will cause other problems including areduction in battery life. Because VRLA batteries need tobe assembled with a controlled plate group pressure toensure long battery life, bowed plates are a far moreserious problem with VRLA batteries than withconventional flooded batteries.

Partly because of this issue concerning bowed plates,the maximum temperature for plate formation should bekept below 40°C. A higher maximum temperature isunlikely to have an adverse effect on plate performance,but there is a greater risk that the plates will bow duringthe formation process. A high current density shouldalso be avoided.


Technical And Theoretical Background

6. Technical And TheoreticalBackground6.1 The formation process explainedThe chemistry that takes place during formation has alot to do with the performance and lifetime of the VRLAbattery in service. It also has a large impact on howbatteries can be processed, particularly in the timesrequired for proper formation. The chemistry takingplace during formation can be characterized on asimple level as follows. [Theoretical treatments can befound in textbooks written by Hans Bode (Lead-AcidBatteries) and Dietrich Berndt (Maintenance-FreeBatteries, 2nd Edition) ].

The purpose of the formation process is to convert thepasted plates to lead dioxide at the positive and lead atthe negative. After pasting, both positive and negativeplates have essentially the same composition, exceptthat the negative plates contain additional “non-leady”additives (negative plate expanders and floc). Thechemical composition of both the positive and negativeplates after pasting and curing is essentially leadmonoxide (PbO), monobasic lead sulfate (PbO.PbSO4),and tribasic lead sulfate (3PbO.PbSO4) [TRB]. Thepositive plate may also contain some tetrabasic leadsulfate (4PbO.PbSO4) [TTB]. The relative proportions ofTRB and TTB are important for formation because TRBpastes form much more easily than TTB pastes. TTB isformed during the plate curing process at temperaturesof ~ 70°C or above. TTB can also be unintentionallycreated during the filling process if the internal batterytemperature is at or above 70°C for an appreciableamount of time.

When the unformed plate is immersed in lead sulfate,the acid reacts with the lead monoxide and basic leadsulphates as shown below:

PbO + H2SO4 PbSO4 + H2O

PbO.PbSO4 + H2SO4 2PbSO4 + H2O

3PbO.PbSO4 + 3H2SO4 4PbSO4 + 3H2O

4PbO.PbSO4 + 4H2SO4 5PbSO4 + 4H2O

A significant amount of heat is generated in thesereactions, and the higher the initial acid density, thegreater the heat that is generated. Sulfuric acid isconsumed in the reactions, so there is also a reductionin acid density. The pastes are largely converted toneutral lead sulfate on their surfaces. These conditionsincrease the resistance of the unformed battery tocurrent flow. The use of 10% or more of red lead in the

positive paste and/or 2-5% of graphitic carbon in thenegative paste provides some conductivity to aid withcurrent flow. Sodium sulfate in the electrolyte (typically1.5% by weight of electrolyte) is also useful in improvingconductivity. Some manufacturing processes alsoinvolve having a small amount of sodium sulfate in thepastes themselves. All of these measures are moreimportant in thicker-plate VRLA designs (platethicknesses and plate spacings >~2.0 mm), as nominalresistance values are higher in such products. Even withthe above materials being present, there is a stronginitial resistance to current flow. Because of this,formation algorithms often start with a short, low-currentstep; immediate use of higher currents can result inheavy gassing from water decomposition due to thehigh voltage needed to overcome the high batteryresistance.

When the electrical current is switched on, theelectrochemical reactions which take place convert thelead oxide and lead sulfate to lead dioxide (PbO2) at theanode (positive plate) and to lead (Pb) at the cathode(negative plate). In some products, formation is from thegrid strands out toward the plate surfaces and in othersit is the opposite. However, in both cases the leadsulfate-active material conversion also results in theproduction of sulfuric acid from the water present in theplate pores and separator. This creates a stronglyconducting environment in the plate stack so that highercurrents can be applied at low voltages.

2PbSO4 + 2H2O Pb + PbO2 + 2H2SO4

2PbO Pb +PbO2

Sulfuric acid is regenerated during the electrochemicalreactions, and because some sulfate was present in thebasic lead sulphates of the cured plates, the final aciddensity at the end of formation is higher than that of thefilling acid.

For a significant period of time, the conversion of leadsulfate to active materials proceeds with very highefficiency, close to 100% in some cases where the rateof water diffusion into the plate pores is high enough tokeep up with the current flow. This is a critical stage information, as the basic pore structure of the plates isestablished as the chemistry proceeds. High-inrushcurrents (following a short, low-current step to promotecurrent flow) are felt to be useful because they createmore seed crystals in the positive paste and a higher-porosity lead dioxide structure is created; seed crystalformation is also aided by the use of red lead as



6.2 Formation processes and Ah input(Additional information about lead acid battery formationof conventional “flooded” batteries is given in theDigatron/ Firing Circuits brochure “Lead Acid BatteryFormation Techniques” by Dr. Reiner Kiessling).

For conventional flooded batteries, the choice offormation processes is as follows:

1. Plate formation. See Section 5 for details.

2. “Two shot” jar formation (also known as boxformation). The battery containing dry unformedplates is assembled into the final container. Thebattery is filled with dilute sulfuric acid (e.g. 1.120s.g.) and subjected to a formation charge: this canbe a stepped charge to control the maximumtemperature (smooth out temperature peaks) andmaximize formation efficiency. After formation iscomplete, the acid is tipped out, and replaced witha higher density acid. Because some of the lowdensity acid is retained in the plates andseparators, the density of the acid for refilling mayneed to be as high as 1.350, to achieve a finaldensity of 1.280. A short equalizing charge for 2hours at a low current is desirable in order to mix theacid before the battery is finished and dispatched.Because the acid is more restricted in jar formationthan in plate formation, additional care needs to betaken to avoid excessive formation temperatures.

3. “One shot” jar formation. This is now generallypreferred over “two shot” jar formation. The batteryis filled with acid of density such that the densityafter formation is the correct density for batterydispatch without the need for further acidadjustment. The required filling acid density willdepend on the battery design (e.g. interplatespacing, active material to acid ratio etc.): forexample typically 1.230 to achieve a final aciddensity of 1.280. Extra care needs to be taken withone-shot formation compared with two-shotformation. The higher density filling acid results in ahigh battery temperature during the first hour afterfilling, because of the vigor of the exothermicreaction between the acid and the active materials.The formation regime needs to be designedcarefully: possibly including one or more restperiods so that the peak temperature does notexceed 65°C. Also, a higher ampere hour input maybe required than for two-shot formation because theefficiency of conversion of the positive activematerial to lead dioxide is poorer the higher thedensity of the formation acid.

described above (the red lead formula is Pb3O4 andeach molecule contains one molecule of PbO2).

The conversion efficiency is greater at the negative platethan at the positive plate. Negative plates form relativelyeasily and it is almost always the positive electrodewhose formation efficiency is poorer. Thus, at some pointrelatively early in formation the positive charge efficiencywill decrease and gassing will begin. If individual platepotentials are monitored during formation, it will beobserved that there are two clearly defined potentials forthe negative plate. At the higher potential (+0.1 to +0.2vwith respect to a cadmium reference electrode), leadoxide and lead sulfate are being reduced to lead. As theconversion process nears completion, there is a rapidchange of potential to about –0.2/-0.3v, at whichpotential the evolution of hydrogen gas by electrolysis ofwater becomes the predominant reaction. However, forthe positive plate, the difference between the potential atwhich the lead dioxide is being formed and the potentialat which competing gassing reactions occur is lessclearly defined. The plate potential is always very closeto that at which the electrolysis of water can occur.Therefore the formation process is inherently lessefficient than at the negative plate. The positive platepotential (with respect to a cadmium referenceelectrode) at the end of formation is about 2.35-2.4v.

Because the plate interiors are only partially wetted byelectrolyte during the filling and fill-to-form processes,the complete conversion of pastes to active materialsvia lead sulfate formation depends upon continuouspenetration of the acid generated by electrolysis into theplate interiors. When heavy gassing in the late stages offormation physically expels acid from the plate poresthis continued diffusion is limited. For this reason, restsor discharges are desirable in VRLA formations,particularly those carried out in an acid-starvedcondition.

The overcharge processes result in the loss of oxygenand hydrogen gases in a 1:2 ratio equivalent to a givenamount of water. This concentrates the initial electrolytestrength and reduces the liquid volume. A moderatewater loss is unavoidable, but if this loss is substantialadditions of water or electrolyte following formation mustbe made.



Typical ampere-hour inputs in relation to wet pasteweight and dry cured paste weight are given in TTTTTableableableableable11111 below. These figures should be used for guidanceonly as they will be influenced by a number of factorsin relation to the plate and battery design andformation regime.

Table 1Ah/kg wet Ah/kg dry

paste weight cured weightTheoretical 200 226

Plate formation (1.100 s.g.) 275 310

2-shot jar formation (1.13 s.g.) 300 340

1-shot jar formation (1.23 s.g.) 350 400

VRLA jar formation 350+ 400+

For guidance, the Ah input in the above table for VRLAjar formation is approximately equivalent to 4x the 5 hourrate capacity, dependent on the battery design andactive material density. It is possible that certain VRLAbattery designs may require higher Ah input than givenin the table above, and extended formation times.However, any increase in Ah input should be minimizedby experimentation to establish the optimum formationregime (e.g. by including brief rest periods or even abrief discharge partway through formation). If choosingjar formation, the battery manufacturer will normallychoose 1-shot rather than 2-shot formation. This is inspite of the fact that VRLA batteries tend to be specifiedwith a higher final acid s.g. which therefore requires ahigher filling acid s.g, resulting in greater heatgeneration during filling. However, on balance there isno particular benefit in using a 2-shot jar formationprocess, because of the difficulty of controlling acidvolumes and final acid density. (Section 3.13 hasalready given sample formation algorithms and profilesfor VRLA jar formation).

6.3 Key Differences Between Flooded andVRLA BatteriesThe comments below relate to VRLA batteriescontaining special separators generically known as“Recombinant Battery Separator Mats (RBSM)”. Theseare typically glass separators also referred to as“Absorptive Glass Mat” (AGM) or “Microfine Glass”(MFG). However, other separator types may also beused, for example containing a blend of glass andpolymeric fibers. A discussion of gel VRLA batterieswill follow later (section 11).

■ The valve-regulated battery is designed so that anygases generated during charge are recombinedwithin the battery. Each cell contains a self-sealingvalve that vents gases to atmosphere if the pressurewithin the cell rises above a preset limit. So the cell/battery is not hermetically sealed but is valveregulated.

■ The separator (normally of microfine glass)completely fills the space between the electrodes.The sulfuric acid is contained within the pores of theplates and the separators and there is no “free” acid.

■ The separator is not quite fully saturated with acid(e.g. 95% saturation), so that any oxygen gasgenerated from the positive plate is able to passthrough unfilled pores in the separator andrecombine with the active lead surface of thenegative plate.

■ As a result, the VRLA battery is unspillable,maintenance free throughout its design life, and canbe operated in any orientation.

■ In the jar formation of VRLA batteries, the cell orbattery is not normally sealed until the formationprocess is complete and the separator saturationlevel is deemed to be correct. Therefore in “open”formation (section 3.3) the recombination process isnot an issue. However, because the separatorcompletely fills the space between the plates, thecell design and the properties of the separator havea critical influence on the acid filling and formationprocess. Since there is also less acid in a VRLA cellthan in a conventional flooded cell, thermal effectsare also more important. (Sealed formation is dealtwith in section 7.1).

■ Cell/ battery reproducibility & variability is also muchmore of an issue with VRLA batteries thanconventional flooded batteries [5]. To make cells asuniform as possible in the manufacturing process,electrolyte amounts are accurately metered into thecell/ battery elements in the filling operation.However, normal tolerances in upstream processes& materials e.g. grid casting, pasting, separatormaterials may result in plate groups with variableamounts of void space within fixed case dimensions.As a result, the filled and formed cells may haveslightly different void volumes. In subsequent duty,the cells may behave slightly differently during thecharging process due to the small differences in theavailable void volume, and cell-to-cell differences inthe compressed separator structure.


Additional information about Jar formation

7. Jar Formation – AdditionalInformation7.1 Battery Preparation for Formation –Sealed FormationThe first part of this brochure (section 3) dealt with“open” formation, which is the more popular and widelyused technique. It is also possible to have the batteryacid-starved and fully sealed during formation. This willdepend upon the battery design and size and the typeof thermal management contemplated. For efficiency ofmanufacture and to minimize handling it is preferable toform a product in the starved state fully sealed. Thus,following formation the battery can be checked forquality, be electrically tested and, if passed, be shippedto the customer with minimal handling. However, thereare stringent requirements on the design and processingof a battery subjected to sealed formation.

In order to be able to form a battery sealed, theprocessing must be such that little or no carbonation ofthe plates has occurred (formation of lead carbonate byreaction of the lead oxide in the paste with CO2 from theatmosphere); carbon dioxide liberated as the platesform can cause expulsion of acid through the vent valvein the form of acid spray. The battery must also be filledto a starved condition with no more than ~95%saturation. Forming sealed, weight losses are minimal(~5% of the fill weight) so that there is only a smallincrease in specific gravity relative to the nominal level.Because of the low gassing levels, heat dissipation fromgassing is low, so for large batteries more care must begiven to keeping the battery in the prescribedtemperature range. If this is not done, acid spray mayagain result due to elevated temperatures in the batteryduring the gassing phase of formation. In practice, thereare very few VRLA products that are formed sealed, dueto the above issues. While it is desirable and can bedone, the cost penalties must be weighed against theease of processing during and after formation.

As noted above, it is relatively difficult to design andprocess VRLA products so that they can be formedsealed. Without adding electrolyte after formation, it isdifficult to achieve a roughly 95% finished saturationlevel without having acid leakage and spray duringformation. The starting saturation needs to be at 97-98%, so unless the battery has a large headspace thereis likely to be physical loss of acid. This may also be thecase if a low surface area or a hybrid glass/organic fiberseparator is used in the battery design. Such separatorsdo not “hold” electrolyte as well as a high-surface-area

AGM material and thus the headspace is easily flooded.In order to handle the acid that is forced into the headspace during the gassing phase of formation, somemanufacturers use devices fitted into the filling port totake up the expelled electrolyte; when the formationcurrent is reduced or terminated the acid can then flowback into the battery and be retained. This approachalso minimizes gassing water loss because when theoverflow device has taken up acid the plate stack andseparator have enough void space to allow for asignificant amount of oxygen recombination. Becausean accurately measured amount of electrolyte can beadded at filling, the final saturation level can also beknown precisely from the materials amounts and theformation weight loss. The external device toaccommodate free acid during formation returns theacid to the battery when gassing is completed; the re-absorbed electrolyte amount then results in anaccurately known saturation level. Following formationthe vent valve is put in place and the assembly of thebattery is completed.

7.1.1 Plate Curing and Carbonation7.1.1 Plate Curing and Carbonation7.1.1 Plate Curing and Carbonation7.1.1 Plate Curing and Carbonation7.1.1 Plate Curing and Carbonation

A detailed discussion of plate curing is outside thescope of this document. However, if sealed formation isproposed, certain precautions need to be taken tominimize carbonation. This is also important if highvacuum filling is used. The reaction of CO2 with the platepastes is actually more likely to occur not during thecuring process itself but after drying, when the platesare taken out of the curing ovens. To minimizecarbonation, plates should be cooled down in a dryenvironment when removed from the ovens (~ 20°C and~ 10% RH). Plates should also be used as soon aspossible after drying. The use of a desiccation systemon the drying oven may also help.

7.2 Acid fillingThe glass mat separator has a critical role in electrolytefilling. Any change in the physical properties of thismaterial can drastically change the quality of the filledand formed cell or battery. The separator structure,degree of compression and fiber composition have asignificant influence on how well an unfilled element willaccept electrolyte. While high levels of compression aredesirable for extended life, this may make the filling andformation process more difficult. When the separator iscompressed, the pore size is reduced, and the spaceavailable for electrolyte between the plates is alsoreduced. This will make the filling process more difficult.(Section 8 gives more detail concerning separatoroptimization).



The Filling Process Within A Vacuum AndNon-Vacuum Fill.

Figure 10

Pre-Fill Stage

Vacuum Process Non-Vacuum Process

Plate pores, separator are evacuatedof all air bubbles.

Plate pores, separator are filledwith air.

Electrolyte Added

Separator is open, all platepores are accessible, rapid

reaction ensues.

Ingress of acid is impededby air bubbles, slower rate

of acid with pastes.

Conceptual View Of the Filling Process ForA VLRA Cell.

Figure 11

Fill Electrolyte

Dryarea?

Separator

positiveplate

“sponge”

negativeplate

“sponge”

interplate spacing, d

plat

e he

ight

, I

When I/d is high, proper filling is difficult or impossible

FigurFigurFigurFigurFigure 10 e 10 e 10 e 10 e 10 is a schematic view of what happens invacuum and non-vacuum filling processes (section3.1). A high-vacuum fill allows faster acid ingress,therefore shorter filling time and higher productivity.However, because it removes air from most of theplate pores, it greatly increases the reactivity and thusthe rate of heat generation [6]. The battery design andmanufacturing process need to be able to cope withthis rapid surge of heat.

When electrolyte is added to the cell, the ideal situationis that all areas are wetted as much as possible by thesame amount of acid so that there is perfectly uniformdistribution of electrolyte throughout the plate stackwhen the filling process is completed. This idealsituation is difficult or impossible to achieve in practice,as there is a dynamic competition between theseparator and the plate surfaces for the electrolyte [6](as shown in figurfigurfigurfigurfigure 11e 11e 11e 11e 11). As the electrolyte penetrates intothe plate stack, it is held up by the separator (thecapillary forces tend to hold the electrolyte fairlystrongly), and at the same time the electrolyte isdepleted by the exothermic reaction of the sulfuric acidwith the plate pastes. As the liquid front penetratesdeeper into the stack it becomes more dilute and also

gets hotter, due to the exothermic reaction with the platepastes. In the extreme case this heat build up cangenerate steam, which will impede the further ingress ofacid/water, and if severe enough may also causebuckling of the plate stack [6]. (FigurFigurFigurFigurFigure 12e 12e 12e 12e 12)

Another danger is the formation of hydration shorts/dendrites. As the acid reacts with the plate pastes, thesulfuric acid electrolyte becomes progressively moredilute. Lead sulfate is relatively soluble in the hotelectrolyte with a pH close to that of water, and solublelead sulfate will diffuse into the separator. This willhasten the formation of lead dendrites and/ or hydrationshorts. A short circuit may develop and be detectedduring formation, or more subtly the battery will failprematurely in service due to the formation of leaddendrites. Sodium sulfate is a useful additive to help toprevent dendrite formation: however during the fillingand formation process the common ion effect may notbe strong enough to prevent dendrite formation if theelectrolyte turns to hot water during the latter stages ofthe filling process.

If the filling process is poor, individual cells may alsohave “dry areas” after filling in which little or no liquid ispresent. These dry areas will slowly become wettedduring and after formation, but massive grid corrosionmay result due to the high temperatures and alkalineconditions prior to and during formation.


Heat dissipation can be aided by the following options:■ A cell design with a high surface area to volume

ratio, which allows a longer time for acid ingress,and thus a longer time for heat dissipation.

■ Chilling of the unformed element and/or electrolyteprior to filling. Chilling the electrolyte will be moreeffective than chilling the unfilled elements.

■ Chilling of the filled element, using water ratherthan air cooling due to its greater heat capacity.

Dendrite growth and grid corrosion result from poor acidingress and distribution. The following factorsare important in promoting faster, more effectiveacid ingress:

■ Minimize heat build-up and steam formation.■ Avoid significant “carbonation” of unfilled elements

by taking special care in the drying and cooling ofthe unformed battery plates.

■ Use a “fluffier” more open separator with a lowergrammage for a given caliper. However, this mayhave inferior compression characteristics, withimplications for battery life.

■ Use a high or rough vacuum fill.

■ Use multiple fill ports and channels in the batterycase to guide acid and remove the “y” factor.

■ Use push/pull massage after electrolyteintroduction.

■ Use a lower surface area AGM: but this may havean adverse effect on performance.

■ Reduce compression to create a higher mean poresize: but depending on the battery application thismay have an adverse effect on battery life.

■ Use more separator and more electrolyte so thatthe heat-sink properties are improved.

Unfortunately, design or materials changes that improvebattery performance and/or life also tend to make properfilling more difficult. This includes e.g. high surface areaglass fibers, high levels of compression, and thin platedesigns. Thin plate designs make possible the creation ofsmall, powerful batteries. But they also mean highersurface areas, smaller interplate spacing and generallygreater l/d ratios (section 10.1). These impact negativelyon the filling process, therefore extra care needs to betaken in filling and formation, to avoid tipping over the“knife-edge” into battery problems.

Action On The Leading Edge Of The Liquid In A VRLA Cell Filling Process.

Figure 12

Fill Electrolyte

PbSO dissolves inhot water, releasessoluble PB(II) intoseparator

pressure, heatfrom steam maybuckle plates,soften and bulgeplastic case

Positive Pasted Plate Negative Pasted Plate

paste particles aredislodged by steam,stain separator

liberated CO2 fromcarbonated pastesexerts back-pressureon electrolyteexpander is leachedout by hot water

Pb(II)

Pb(II)

hydration shorts,dendrites

Hot WaterSteam

Separator



7.3 Control of Formation TemperatureThermal management of the battery must be tailoredto its size, the type of filling process and the formationconditions used. Obviously, there is no set formula forall VRLA products, so handling of batteries prior toand early in formation must be developed by themanufacturer. In general, it can be said that very smallVRLA batteries (25Ah or less) are much more tolerantof temperature and cells more so than 6 or 12Vbatteries; for these products minimal thermalmanagement is required (but the risk of over-cooling ishigh). For larger products the thermal requirementsbecome more stringent and in the 60-100Ah range,particularly in multi-cell batteries, great care must betaken that the batteries are adequately cooled, but arenot cooled too much.

The VRLA battery manufacturer could use thefollowing checklist in order to determine the necessarytemperature control to apply:

■ The size of the product (i.e., single cell or 6/12Vbattery)

■ The battery envelope (i.e., the surface-area-to-volume ratio for heat dissipation).

■ How has the battery been handled prior to thestart of formation?

■ Battery temperature at the start of formation■ How will the batteries be cooled or heated

during formation (ambient, forced air, water,circulated water)?

■ What is the plant temperature (air conditioning,summer or winter)?

■ How much heat will be generated in theformation process and what is the duration?

■ Is the battery formed sealed or open, starved orflooded (i.e., what are the contributions of theoxygen cycle to heat generation and of gassingto heat dissipation)?

The smaller the battery and the higher the surface-area-to-volume ratio the more easily heat is dissipated.In the extreme, heat dissipation may be so good thatsmall VRLA products actually require heating duringformation! This is particularly true in a plantenvironment with poor temperature control i.e., hot inthe summer and cold in the winter. Small VRLAbatteries require a minimum temperature for efficientformation and a maximum above which damage canoccur. At the low end, formation of the PAM can be so

poor that the degree of formation and initial dischargecapacities are reduced. It is an unfortunate fact thatnegative plates are formed best at temperatures of40°C or less; positives form better at highertemperatures. When positives are formed below 40°Cthere is an increase in the alpha-PbO2 content, adecrease in total PbO2 and a fine pore structuresusceptible to clogging by lead sulfate duringdischarge can result. Because of all of these factors, agood formation system for small VRLA productsshould include some form of forced, circulated air thatcan be either heated or cooled, depending upon theambient plant conditions, the product size and shapeand the amount of heat production at each stage offormation.

Larger batteries (25-100Ah), particularly those withunfavorable envelopes for heat dissipation (a cubicstructure is the worst case), almost always requirecooling during formation. This is necessary to avoidhigh damaging temperatures and also to haveuniformity of temperature among the cells in a 6- or12V battery. In the best case (small size, favorableenvelope, long low-current formation) passive cooling(radiation, convection) can be employed, but there islikely to be a large swing in product quality betweensummer and winter conditions unless the plant has anoutstanding air-conditioning system. It is more likelythat active cooling will have to be employed and thiscan range from forced ambient air to forced chilled airto stationary water bath to chilled, circulated waterbath. The use of water for cooling compared to air issignificantly more efficient due to the higher heatcapacity (four times that of air) and thermalconductivity (roughly 15 times greater) of water.Overall, heat transfer away from batteries duringformation is roughly nine times more efficient for waterover air. Clearly, water is preferable to air for a numberof reasons but it usually involves a higher capital inputand more maintenance. In some cases it may not benecessary, but perhaps the best argument for its useis that with the efficient cooling of circulated watershorter formation times can be used for someproducts, thus maximizing the capital input forformation equipment. Different products will eachrequire a specific type of temperature control.



Several examples of the relative effects of air andwater cooling are shown in FigurFigurFigurFigurFigures 13es 13es 13es 13es 13 and 14 14 14 14 14 forseveral different battery sizes. These figures comparecell and battery temperatures with differentcombinations of chilled and room-temperatureelectrolyte and the use of air and water during the fill-to-form period. As can be seen, there are significantdifferences in heat dissipation using air and water andthis also applies during formation [7].

Thermal management during the formation processitself is also very important. As noted earlier, at thebeginning of formation the battery resistance is quitehigh and if high inrush currents are employed ohmicheat generation can be substantial. The formationreaction itself is highly exothermic, as is the continuingoxide/acid neutralization reaction that takes place asacid generated by electrolysis penetrates deep intothe plates as formation proceeds. The heat of reactionfor the formation process is ~394 kJ/mole and the heatof neutralization is ~161 kJ/mole – both of which aresubstantial. Later in formation the overchargeprocesses of water decomposition and hydrogen

evolution begin and this also contributes to a highertemperature level. If the battery is formed in the starvedstate there is a further contribution to heat generation bythe oxygen-recombination reaction involving oxygenreduction at the negative electrode. Finally, if the batteryis formed sealed heat dissipation due to gassing isminimized, whereas maximal heat dissipation occurs ifthe battery is formed in a flooded state and/or is open tothe atmosphere.

To some extent the formation algorithm can be used tocontrol the temperature during the formation process,and smooth out temperature peaks. For example, longerformation times at lower currents not only minimizeohmic heating but they also provide longer times forheat dissipation. This is usually in conflict withmanufacturing pressures, which favor the shortestpossible formation times. The use of rests or dischargeswill provide time for heat dissipation, but they alsolengthen formation. However, there are other technicaladvantages to these steps as discussed in section 3.13.

2.5 Ah And 25Ah Spiral-Wound Single-Cell Internal Temperatures During Different Fill-To-Form Conditions.

Figure 13

A D cell (2.5 Ah), 20minutes in 10ºC cooland wash, balance in23º air.

B BC cell (25 Ah), 30minutes in 10ºC cooland wash, balance in23º air.

C BC cell, air cooling(23ºC) only.

D BC cell, electrolyte at10ºC, 30 minutes in10ºC cool and wash,balance in 23ºC air.

Time After Fill, Minutes20 40 60 80 100 120 140 160 180 200

Tem

pera

ture

, ºC

140

120

100

80

60

40

20

0

AD

CB



7.4 Completion of formation

In theory, formation is complete when there is conversionto 100% lead at the negative and 100% lead dioxide atthe positive, but this is not possible in practice. Therequired degree of conversion will also depend to someextent on the battery application. Close to 100%conversion may be possible for the negative plates, butis more likely to be in the range 90-95% conversion tolead dioxide for the positive plates. A lower PbO2

percentage may be acceptable for SLI batteries becauseit is assumed that the battery will be used fairly quicklyand even though it is not completely formed the batterywill be able to start the vehicle. In addition, the shallowdischarge service will slowly help to complete formation;because the battery is usually charged by the alternatorat a relatively low voltage and will typically only be at 60-70% state of charge in use. On the other hand, manyindustrial batteries are required to deliver nearly 100% ofrated capacity when they are put into service by the enduser; in addition, they may be held on the shelf for longperiods of time before they are commissioned (thusrequiring very low levels of unformed oxide whichequates to a low self-discharge rate). Because of theseconsiderations, “completeness of formation” must berelative to the product and its intended use.

7.5 Alternative Jar Formation OptionsThe battery manufacturer may wish to consider somerather more unusual assembly/formation options toovercome some of the disadvantages of jar formationalready mentioned.

One option might be to place the assembled plategroup in a container which is larger than the finalcontainer so that the plate group is under little or nocompression during formation. After formation, surplusacid is drained off, and the plate group is placed in thefinal container to give the required degree ofcompression/plate group pressure. This approach wouldeliminate the problems already mentioned, which canoccur when formation is attempted with a high plategroup pressure. In particular it would eliminate theproblem of changes in plate group pressure during theformation process (arising from changes in the volumeof the battery plates during formation).

6V/100 Ah Prismatic Battery Temperature Data (Middle Of Center Cell) During Fill-To-Form Time With Different Conditions.

Figure 14

A Room temperatureelectrolyte.Cooling water at 8ºC.

B -20ºC electrolyte.Cooling water at10.5ºC.

C -20ºC electrolyte.Cooling in air at 21ºC.

Time After Fill, Minutes20 40 60 80 100 120 140 160 180 200

Tem

pera

ture

, ºC

110

100

90

80

70

60

50

40

A

C

B 47ºC at360 Min.



Battery and separator design guidance

8. Battery DesignThe battery design has a critical influence on the fillingand formation of VRLA batteries. Some of the potentialproblems with VRLA battery filling and formation can beminimized or eliminated by careful battery design.Unfortunately, some of the design strategies to improvefilling and formation may have an adverse effect onbattery performance and life, so some compromise maybe necessary.

The battery design parameters which may influenceVRLA cell/battery filling and formation include:

■ Battery height: tall batteries are harder to fill thanshort ones.

■ Battery width: short, wide batteries are moredifficult to fill if filled from a single filling port.

■ Plate thickness and interplate spacing■ Plate height and plate height/interplate spacing

ratio■ Filling port position■ Battery case draft■ Active material additives (expander/reinforcing

fibers)■ Gravity: liquid will only wick so high before being

defeated by gravity: not a factor in gravity filling(top to bottom).

■ Separator properties:- Volume porosity and pore structure (mean pore

size). Finer pores wick more slowly but to greaterfinal heights

- Saturation- Compression: results in a finer pore structure with

high tortuosity, therefore slower wicking. Forexample, 15% compression will double wickingtime to a given height.

- Caliper (thickness at defined pressure)- Grammage (g/m2)- Surface area/ fiber diameter. Finer fibers (higher

surface area) result in finer pores, hence slowerwicking.

- Wettability- Fiber structure (coarse/fine fibers; inclusion of

synthetic fibers). Organic fibers inhibit wicking(not wetted by sulfuric acid), and also promotefaster drainage.

- Fringe area of separator (area of separator notcovered by plates)

It can be seen that the separator properties are critical,and these are discussed in more detail in Section 9. Theother critical battery design parameters are discussedas follows.

8.1 Plate height/plate spacing ratio (L/d)The ratio of plate height to plate spacing (L/d) can beused as a rough measure of the difficultiesencountered in filling. For a L/d ratio equal to or lessthan 50, easy filling results. If the ratio is between 50and 100, care should be taken to avoid potentialproblems. Filling becomes more difficult when theratio is between 100 and 200, and is almostimpossible at ratios above 200 [8]. It can be deducedfrom this that the worst case is a tall battery with aclose plate spacing: the best case is a short, narrowbattery with a wide plate spacing.

8.2 Battery case draftBattery case draft can result in a 10% compressionchange from the top to the bottom of the plate. Forexample, with a target compression of 25%, thecompression may actually vary from 20% to 30%between the top and bottom of the plate. The effect ofthis on the performance and life of the battery may behighly significant. This effect should not be ignored inthe formation process as well. The separator at thebottom of the cell will be subject to a highercompression resulting in a smaller pore structurewhich will influence the speed at which the acid fillsthe separator during the acid filling process: there willbe a slower acid drip speed as the acid approachesthe bottom of the plate. Because smaller poreshave a greater force to pull liquid, this may alsoincrease stratification. [9], [10]. There is a sloweracid drip speed as the acid approaches the bottomof the plate.

8.3 Active material additivesAdditives in the active material can also affect thefilling operation. The expander or reinforcing fibers inthe paste may interact and result in excessivegassing during acid addition. This will result in alonger fill time or even in an unacceptable product.Care needs to be taken when any new material isused since the VRLA battery should be considered asa system and all the ingredients interact.



Solubility Of Lead Sulfate In Sulfuric Acid At 25ºC.

Figure 15

Density of Sulfuric Acid (mg/liter)

Solu

bilit

y of

Lea

d Su

lfate

(mg/

liter

)

7

6

5

4

3

2

1

01 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4

8.4 Electrolyte additivesMost VRLA battery manufacturers use sodium sulfateas an additive to the electrolyte. It is added to theelectrolyte in powder form, at about 1% by weight.Sodium sulfate acts by the common ion effect toprevent the harmful depletion of sulfate ion which is adanger in the discharge of acid-starved batteries.The addition of sodium sulfate provides an“inventory” of sulfate ions that are available withoutincreasing grid corrosion [11]. The solubility of leadsulfate increases significantly as the concentration ofthe sulfuric acid electrolyte decreases, as shown infigurfigurfigurfigurfigure 15e 15e 15e 15e 15. The solubility increases more thanfourfold as the sulfuric acid density decreases from1.300 to 1.100 kg/l. Under certain conditions ofover-discharge, the amount of dissolved leadsulfate may be such that on recharging the reducedlead will form metallic bridges between the plates.The addition of sodium sulfate will reduce this risk.

Alternative electrolyte additives may be used, whichhave a different mode of operation. This class ofadditives is known as dendrite prevention additives(DPA) [13]. These operate by actively seeking outand deactivating the lead dendrite growths. They arepolar organic compounds that are believed todeactivate a growing lead growth by coating its tipwith a layer of oriented molecules. Once the leadgrowth is deactivated, these molecules are availableto move onto the next site.

9. Separator OptimisationThe separator properties have a critical impact on acidfilling and jar formation [6]. Any change in the physicalproperties of this material can drastically change thequality of the filled and formed cell or battery. The typeof separator used is dictated more by the intendedbattery application, but its properties can also partiallydetermine the filling and formation conditions used.

During the filling process the acid wicking rate isimportant. The acid wicking rate is primarily a function ofthe mean pore size of the glass-mat separator; this, inturn, is largely a function of the fiber mix (represented bythe fiber specific surface area as measured by BET), thedensity of the glass mat and the compression level inthe unfilled plate stack. In practice, wicking is onlydirectly applicable for “top-down” gravity and “bottom-up” filling methods where wicking is the primary mode offluid transport. For soft- and hard-vacuum fillingtechniques separator properties also have a role, but thevacuum level and filling speeds are additional controlelements, in addition to the electrolyte temperature andits resultant viscosity. A further variable is the use of 10-20% organic fibers mixed with glass, as in the H&V IIP-15 material (see also section 10). The organic fractionconfers greater tensile strength and it also facilitatesfilling due to the hydrophobic nature of the organicfibers. Since the organic fibers are not wetted by sulfuricacid, the electrolyte is not “held” as strongly as by glassfibers. This clearly facilitates filling, but it can result inflooding of the negative-plate pores with acid andelectrolyte regurgitation and spray may be significantduring formation.

The actual separator compression in the plate group willinfluence the ease of acid filling and jar formation as wellas impacting on the performance of the battery. Highseparator compression has been shown to be beneficialin extending the life of VRLA batteries by inhibitingpositive plate expansion, but unfortunately the processof filling the battery with acid becomes more difficult.When the separator is compressed it reduces the poresize significantly and also reduces the space availablefor electrolyte between the plates. This adversely affectsthe wicking properties of the electrolyte. However,smaller pores and higher compressions may mitigatevariations in saturation and acid strength in the verticalplane (stratification). It is also important to optimize theratio of plate and separator pore volumes to ensuresufficient electrolyte.



The easiest filling is achieved by using a combination ofglass and organic fibers with a low specific surface area(~0.8-1.4 m2/g) in a low-density material (i.e., highpercent porosity of ~95% or more) that has a relativelylow compression level (25-30 kPa dry or less) in theassembled, unfilled plate stacks. This gives an openstructure that is not completely wetted by the electrolyteand, thus, has the best chance for uniform fluiddistribution. This type of separator would be best suitedto gravity filling. However, this type of separator and cellconstruction also is most susceptible to electrolytedrainage and stratification, particularly in deep-cyclingapplications. On the other hand, the best type ofseparator to minimize drainage and stratification is ahigh surface-area glass (~2.0-2.6m2/g), high density(90-92% porosity) all-glass with high compression. Thiswill give excellent deep-cycling results but it is extremelydifficult to fill, particularly in large batteries. One mightthink that a high-vacuum fill would be best for this typeof separator but, in fact, this would only be true inrelatively small VRLA batteries (~25Ah or less) due tothe large amounts of heat generated in short times inhigh-vacuum fills. If the battery configuration cannotdissipate the large burst of heat generated by the fillingprocess there can be permanent damage in the form ofplate buckling, separator staining by paste and/orexpander, bulging of the case and destruction ofterminal seals; internal cell temperatures in excess of110oC can be achieved for relatively long periods oftime. Gravity fills with this type of separator system willtake much longer times (possibly up to 30-40 minutes),but thermal issues will be minimal.

In the formation process itself the separator can have aninfluence on gas management and electrolytedistribution. The importance of this influence will dependin part on whether “open” (section 3.3.1) or “sealed”(section 7.1) formation is used. For open formations, thetype of separator used is not critical, as provisions areavailable for gas escape and fluid management,whether by using a completely open top or by havinghollow tubes attached to the cell fill ports. For sealedformations, however, the separator type and amount, thesaturation level, the formation algorithm and the designheadspace are all important. Forming sealed underpressure can obviously lead to acid regurgitation andspray, but it also puts pressure on all of the seal areasand can damage the functioning of some vent valvedesigns by allowing electrolyte to leak into the seal areabetween the valve and the fill stem, possibly leading to

valve “sticking” (where the valve won’t open and releasegas at the design opening pressure).

If a battery is designed for sealed formation, theseparator chosen should have a relatively high surfacearea (~1.6m2/g or more), be all glass and should have atleast moderate compression in the finished plate stack.This is to ensure that the separator reservoir holds itselectrolyte as tightly as possible without havingunacceptably poor filling characteristics. Moreover, theamount of separator per ampere-hour of capacity shouldbe relatively great (1.4-2.0g/Ah) and the saturation levelafter filling should be ~95% or slightly less; it is virtuallyimpossible to form a VRLA battery sealed in the fullysaturated or flooded state. These parameters will allowuse of a sealed formation even with fairly aggressivealgorithms (high currents, short times). However, careshould be taken to minimize heavy gassing by usingmultiple rest periods when gassing potentials arereached. These will also allow more electrolyte to “soak”into the plates and more void space will be created inthe separator, enhancing electrolyte retention.

The rest of this section will give further backgroundinformation concerning the influence of the separatorchoice and separator properties on the filling andformation process. Typical design parameters are givenbelow, and are then discussed in more detail:

VVVVVolumeolumeolumeolumeolumeporporporporporosity:osity:osity:osity:osity: 92%

Saturation:Saturation:Saturation:Saturation:Saturation: 95%

ComprComprComprComprCompression:ession:ession:ession:ession: 30%

Acid utilization:Acid utilization:Acid utilization:Acid utilization:Acid utilization: 8.8 – 9.5 ml/ Ah

SeparatorSeparatorSeparatorSeparatorSeparatorcaliper:caliper:caliper:caliper:caliper: Related to interplate spacing and

required degree of compression

SeparatorSeparatorSeparatorSeparatorSeparatorgrammage:grammage:grammage:grammage:grammage: > 2g/Ah preferred

SeparatorSeparatorSeparatorSeparatorSeparatorsursursursursurface arface arface arface arface area:ea:ea:ea:ea: > 2m2/g preferred to minimize

stratification, but filling will be moredifficult.

Jar forJar forJar forJar forJar formationmationmationmationmationAh input:Ah input:Ah input:Ah input:Ah input: 4+ times rated capacity. It is

necessary to be careful about toomuch overcharge during formation:this may damage the positive platesand increase the overall aciddensity.



9.1 Volume PorosityThis is a very important figure as it will determine howmuch acid the separator will hold and is therefore acritical parameter in the battery design and thedetermination of the battery capacity. For 100% glassseparators, the figure for the volume porosity in thenominally uncompressed state is typically in the range92-95% (as measured at 10 kPa). Compression of theseparator will reduce this by a few percent, so that in thecompressed state it will typically be 90-92%.

There has been some experimentation with “hybrid”separators containing a percentage of polymeric fibers,or non-glass separators such as the Daramic AJSseparator. These separators may have a lower volumeporosity and will therefore hold less acid. This needs tobe taken into account in the battery design.

9.2 Saturation LevelThe cell/ battery is not normally sealed until theformation process is complete and the separatorsaturation level is deemed to be correct (normally 95%)(except for sealed formation, section 7.1). If in doubt, thebattery manufacturer should err on the side of over-rather than under- saturation of the separator. If theseparator is over-saturated, and the cell is then sealed,the recombination process will be less efficient initially,some water (as hydrogen and oxygen gases) will be lostfrom the system, and the efficiency of the recombinationprocess will increase, preventing further water loss.However, if the separator is under-saturated in relation tothe design value, the cell may contain insufficient acid tomeet its design capacity.

An accurate calculation of the amount of acid absorbedby the plates and separator is needed when precisionacid filling is used [12]. The separator needs to be 90-95% saturated, which corresponds to the separator inthe area between the plates holding about 6g of acid forevery 1g of separator. The fringe area of the separatoralso needs to be considered. Larger fringe areas allowfor additional acid and thermal capacity in the battery:this will help in the thermal management of the cell.There may also be some contribution to the low ratecapacity of the cell. The acid gravity is normallybetween 1.290 and 1.320 and for guidance a figure offrom 9 to 11 ml of acid per Ah as measured at the 20-hour discharge rate should be used in the batterydesign calculation. Fully discharged, the acid gravitycan be around 1.08.

9.3 Separator CaliperThere is a standard BCI method for measurement ofseparator caliper (thickness). Because of the “fluffy”nature of the RBSM, the caliper is measured at acontrolled pressure of 10 kPa. Although this may bereferred to as the “uncompressed” thickness, it isimportant to note that this is referenced to a controlledpressure of 10 kPa. Specifications of e.g. “20%compression” or “30% compression” are referenced tothis thickness as measured at 10 kPa. The requiredseparator caliper needs to be calculated in relation tothe interplate spacing and the specified % compression.For example, a battery with an interplate spacing of0.11cm and a design separator compression of 30% willrequire separator material with a caliper of 0.16cm.When compressed by 30%, this separator material willhave a caliper of 0.11cm.

Recent research has highlighted the importance of plategroup pressure rather than % compression as the key toextending battery life (see comments below).

9.4 Separator CompressionALABC research work has shown that high compressionbattery designs can extend battery life by maintaining ahigh pressure against the positive plates and eliminatingor minimizing the phenomenon known as “prematurecapacity loss”. In fact, it may be more relevant to refer to“plate group pressure” rather than % compression.Some recent separator designs are less compressiblebut may be able to maintain a higher pressure againstthe positive plates than conventional glass separators[13]. Unfortunately, a high plate group pressure/ highcompression design may also be more difficult to fill. Ahigher compression will generally result in lower fill rates.When the separator is compressed it reduces the poresize significantly and also reduces the space availablefor electrolyte between the plates. This adversely affectsthe wicking properties of the electrolyte.

Another issue that may need to be considered is thatof changes in plate group pressure during formation.There are changes in the volume of both positive andnegative active materials during the formation processas the lead oxides are converted to lead at thenegative plates and lead dioxide at the positive plates.This may have some effect on the separatorcompression and applied plate group pressure. Thisneeds to be taken into account in the design of thebattery and the specification of the separator and theinitial compression level.



BET Surface Area, m2/g

20

18

16

14

12

10

8

6

4

2

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Mean Pore Size Vs. Kr BET Surface Area.

Figure 16

Mea

n Po

re S

ize (m

icro

ns)

However, recent ALABC research has shown thatunder some circumstances the separatorcompression may drop significantly after formation[14]. The exact causes of this are not yet certain, butmay be related to a relatively low initial plate grouppressure. There may be a critical compression thatholds the fibers in place (for a particular separator)and if there is significant gassing at the end of thecharging process there may be a loss of integrity inthe fiber mat.

While this problem is not yet fully understood, thefollowing design issues need to be considered tominimize the risk of loss of plate group pressureduring jar formation:

■ Assemble cells with the maximum practicableplate group pressure (> 40 kPa)

■ Maximize available acid volume and increaseseparator grammage to >= 2g/Ah.

■ Increase the fine fiber content of the separator.■ Use a formation algorithm that minimizes the

gassing at the end of charge.

9.5 Separator GrammageThe separator grammage is the weight of theseparator per unit area. The amount of acid held bythe separator is very important, therefore separatorgrammage as well as thickness needs to beconsidered carefully in the battery design. The aimshould be to maximize available acid volume, whichwill improve the heat capacity of the battery andenable thermal management to be improved. Theamount (g/ Ah) of separator used will also have animpact on battery processing and performance. Ahigher amount of separator (around 2g/ Ah or greater)will have a beneficial impact on practical levels ofcompression, gas recombination and acidstratification. This also implies a greater plate spacingand larger electrolyte reservoir. This will make it morepractical to carry out jar formation on the completedcell/ battery [15].

9.6 Separator Surface AreaThe surface area of the glass mat is very importantbecause it has a great deal to do with wicking duringfill and fluid movement in fill/formation. There is areasonably well-defined relationship between surfacearea and pore size, as shown in figurfigurfigurfigurfigure 16. e 16. e 16. e 16. e 16. This curvewas constructed from data on various separatorsamples from a wide range of manufacturers [16].

The separator surface area for a glass separator isrelated to the ratio of coarse/ fine fibers. A lower surfacearea (higher proportion of coarse fibers) separator hasadvantages in the filling process, but may have otherdisadvantages depending on the battery application. Ahigher surface area correlates to a smaller pore structureand results in a lower wicking rate, but a greater ultimatewicking height [17]. (Figur(Figur(Figur(Figur(Figure 17)e 17)e 17)e 17)e 17). The smaller porestructure will also help to decrease stratification withinthe cell. The pore structure of the separator provides fora highly tortuous path which helps to prevent dendritegrowth and minimizes the size of any dendrite if formed.However, this also creates a tortuous path for acid andair movement. This increases the filling time for eachcell. A battery designed for deep cycling should use ahigh surface area separator, but extra care will need tobe taken during the filling process. The higher surfacearea separator will require additional time to add theacid, since the acid wicks more slowly through finerpores. Also, the way the acid is added to the battery iscritical. If the acid is added too rapidly from the top, theair within the plates and the separator may not haveenough time to escape, and dry spots may result. If thefilling process allows the acid to wick up the separator,entrapped air can escape since it does not have todiffuse through the electrolyte. It is also necessary toallow sufficient time to allow for complete filling of thepores of the separator. With a high surface areaseparator, an advantage of the longer time for acidingress could be a longer time for heat dissipation. Thefilling procedure is critical to providing a quality VRLAbattery.



Impact Of Surface Area (m2/g) On Water Wicking HeightWhile Under 20% Compression, After 24 Hours.

Figure 17

= 0.8= 1.3= 2.2= Hybrid @ 1.0

Wet

/Dry

Wei

ght o

f Sep

arat

or

8.00

7.00

6.00

5.00

4.00

3.00

2.00

1.00

0 20 40 60 80 100 120 140

Height (cm)

1000900800700600500400300200100

0

Tim

e / s

0(Height)2 / cm2

25 50 75 100 125 150

Note: Strips of AGM not compressed.All AGM samples are singlelayered except AMER-GLASS,a multi-layered AGM.

= 100% Fines= 20% Fines= 0% Fines= AMER-GLASS= AGM(B)= AGM(A)

Slower Wicking

Faster Wicking

Effect Of Fiber Mix And SegregationOn Vertical Wicking Speed.

Figure 18

10. Separator designs to improvewet formationFor many years H & V have marketed a hybrid glass/organic separator Hovosorb II, covered by US patent4,908,828 [18], [19]. This separator contains a syntheticfiber with reinforcing glass strands, the balance beingmicroglass. The synthetic fibers are hydrophobic, andthese hydrophobic sites within the separator matrix offercontrolled wetting properties of the separator andmodification of the recombination process. It is claimedthat this assists the filling and formation process, andallows a “fill and spill” formation technique to be used.The unformed cells can be flooded with electrolyte priorto formation, and drained of excess free electrolyte afterformation. It is claimed that the use of Hovosorb IItogether with a “fill and spill” formation system mayresult in a more uniform cell-to-cell electrolyteconcentration than is obtained with volumetrically filled,in-container formed cells.

With Hovosorb II, because of the hydrophobic siteswithin the separator, recombination can occur evenwhen the separator is fully saturated. This is becausesome pores within the separator remain unfilled, even inthe presence of excess free electrolyte, so that oxygenis provided with a path for transfer to the negativeelectrode surface. Oxygen recombination may even beenhanced at those areas on the negative electrodesurface that are in direct contact with the non-wettablematerial contained in the separator. The separator alsohas improved compression properties compared with100% glass separators. Hovosorb II-P-15 is a refinementof the original Hovosorb II, and has improved punctureresistance.

An alternative approach is to use separators that consistof two or more layers of different fibers: this may behelpful in the filling process since layers of coarse fibersare soaked more quickly. Battery filling is made easierwith an “oriented” separator that has separate layers ofcoarse and fine fibers: the fine fibers against the positiveplate, and the coarse fibers against the negative plate.This has a very fast wicking characteristic both upwardand downward [20] [8]. In figurfigurfigurfigurfigure 18e 18e 18e 18e 18 the influence of fibermix and segregation on the vertical wicking speed isshown. FigurFigurFigurFigurFigure 19e 19e 19e 19e 19 shows the upward and downwardwicking height for oriented and non-oriented fibers.During the filling process, the fine fiber componentabsorbs acid quickly, but when the battery is filled fromthe top, the looser, coarser fiber structure permits an



easier access to the electrolyte which thenpermeates instantaneously to the fine fiber side.When the process is in reverse and acid is spilled outof the battery, the forces binding the electrolyte to thecoarser fiber structure are weaker, so that electrolytewill be preferentially lost from this part of the AGM.The desired partial saturation of the separator is thusquickly reached. This multi-layered AGM such as thatmanufactured by Amer-Sil, has faster wickingproperties which may be of great value in the “grayzone” of filling where the ratio of plate height to platespacing is between 50 and 200.

Another possible option is to include a thin microporoussheet as part of the separator system: this may help toeliminate the problem of lead dendrite formation. Thismight also help to control the diffusion of oxygen fromthe positive to the negative plate. An example of such amicroporous separator is the DuragardTM separatorrecently announced by ENTEK International at 7ELBC inDublin. Amer-Sil has also developed a compositeseparator which includes a microporous sheet betweentwo layers of glass. Results with this separator systemhave been reported in the ALABC ResearchProgramme.

= Non Oriented AGM(mixed fibers)

= Oriented AGM(segregated fibers)

Upward And Downward Wicking Height For Oriented And Non-Oriented Fibers.

Figure 19

80

70

60

50

40

30

20

10

0

UpW

ard

Wic

king

Hei

ght (

cm)

Wicking Time (Min.)50 100 150 200 250 300 350 400 450 500

Compressed @ 10 kPa; band 5cm

40

35

30

25

20

15

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UpW

ard

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Wicking Time (Min.)5 10 15 20 25 30 35 40

Compressed @ 10 kPa; band 5cm


VRLA gel batteries overview

11. VRLA Gel BatteriesGel is an older technology than RBSM technology forvalve regulated lead acid batteries: gel batteries havebeen around for many years but have not been widelyused except for special applications. The gel systemhas an inferior performance at high discharge rates,therefore it is not suitable for applications such as SLIrequiring a high rate discharge capability. The geltechnology may be more appropriate for tall cellsbecause the gel system does not suffer fromstratification problems. The gel is produced by addingfinely divided (fumed) silica to sulfuric acid: theconcentration of silica in the gel is about 6%. Fumedsilica is a high purity silica manufactured by hightemperature hydrolysis of chlorosilanes in a hydrogen/oxygen flame. It is typified by a small particle size anda very high surface area, in the range 200 – 400 m2/g.When the fumed silica is mixed with sulfuric acid, aviscous solution is formed, which develops into athixotropic gel on standing. It has been found that theinclusion of phosphoric acid is also beneficial, thisgives the battery a much longer cycle life, greater thanthe addition of phosphoric acid to a flooded batterydesign. The optimum H3PO4 concentration is17-30g/L. A typical process for preparation of the gelis given below:

6% by weight of fumed silica is added to 1.280 S.G.sulfuric acid with continuous stirring. 20g/ L of 85%phosphoric acid is added and stirring continued.Stirring is continued while pouring the gel into thebattery: the gel will set as soon as the stirring ceases.The battery should be filled under vacuum and stirringshould not be stopped until the gel is in the battery.

Because the gel itself is unable to prevent thepenetration of lead dendrites that can cause shortcircuits between the plates, a conventional separatoris required, which has ribs on both sides of theseparator. Stratification is negligible, because the gelis more strongly fixed in the plates and separators. It isnot possible to carry out jar formation of gel batteries,the battery needs to be assembled with dry chargedplates before adding the gel. Sufficient time needs tobe allowed for the gel to “set up”, and the cells shouldthen be given an equalizing charge. During thisequalizing charge free electrolyte may percolate from

the gel as the gel cracks and shrinks. The free acidcan be removed from the top of the cell before sealingthe cell and this will ensure that the cell is in arecombinant state prior to going into service. Theelectrolyte removed from the cell can be measured toprovide an accurate volume of the electrolyte presentin the cell. The total amount of electrolyte in the gelcell may be slightly less (~ 80-90%) than that added toa comparable AGM cell.

The electrolyte is immobilized in a 3-dimensionalstructure set up by the very fine particles of silica [20].In an aqueous medium, these particles are fixed bythe presence in their midst of negatively chargedsulfate ions. The gel formation happens at a molecularlevel and allows the electrolyte to be present in the cellin an altered state that is neither liquid nor solid. Itdoes not have the required mechanical strengthproperties to separate the plates, therefore amechanical separator is needed. The separator in thegel cell is purely a spacer, similar to the separator in aconventional flooded cell. Gas transfer occurs via voidspaces which develop within the gel structure as itdries out slightly and opens up under the pressure ofthe oxygen gas bubbles. The density of the gel willdepend on the silica content of the gel. The higher thegel density (higher silica content) the harder it will befor crevice creation, and the greater the need for avery open separator.

There may be different consistencies of the geldependent on the silica content of the gel: a “soft” gelhas a lower silica content than a “hard” gel. The “soft”gel will have a relatively weak structure and only verylow shear forces are required to break it. Theconsistency of the gel will influence how many cyclesof discharge/ charge are needed to achieverecombination. Initially when the silica gel is formedthere is total water saturation. The gel structure iscompletely filled with the electrolyte, which is alsopresent in the active material and in the gel/ electrodesurface interfaces. For the first few cycles, the gelledVRLA cell functions similarly to a flooded lead/ acidcell and water loss occurs, particularly at the end ofthe charging periods. As water is lost in the initialcharging cycles, there is a slight dry-out of the gelstructure, which creates micro-channels in the gel


VRLA gel batteries overview / Formation equipment, battery monitoring and product testing

through which gas can pass. The “softer” the initialgel, the sooner the recombination process starts,because the process of gel cracking can start moreeasily.

The formation of the gel is not influenced by thetype of separator used or its design. However, theseparator does have an important influence on thefilling process and the ease of oxygen transportduring the recombination process. The separator forgel batteries is a conventional separator as may beused in flooded lead acid batteries but with someimportant design differences. There are deep ribson the negative side of the separator as well as onthe positive side of the separator. The ribs arenormally vertical and relatively widely spaced topermit easy filling with the gelled electrolyte. Theinterplate spacing is also very important: with a thinplate battery design having a close plate spacing,filling with the gelled electrolyte may be difficult ifnot impossible.

For gelled VRLA cells, the separator porosity needsto be as high as possible. This is because theseparator needs to retain as much of the electrolyteas possible in its structure and to minimize thebarrier to oxygen transport through the separator.The pore size of the separator is also important inthe context of oxygen transport through theseparator. The optimum mean pore size needs to bein the range 1 - 10µ. Separators with a mean poresize < 1µ (µ=micron) severely inhibit oxygentransport through the separator so that the onlyroute for oxygen transport is around the edges orover the top of the cell group. The maximum rate ofthe internal oxygen cycle is lower in gel cells than incells with AGM separators. The maximum rate istypically 10 A/100 Ah in AGM batteries, and 1.5 A/100 Ah in gel batteries [21].

12. Formation Equipment AndLayoutApart from the choice of electronic equipment (rectifiers,power resistors, power supplies, etc.), there are somecritical practical issues in choosing battery connectionsand configuring formation bays. These can have asmuch to do with resulting product quality and uniformityas the choice of an effective formation algorithm.

12.1 Battery Connections

This topic is often neglected, but in practice can have alot to do with product uniformity and scrap levels. Thereare several common methods of hooking units togetherin a formation bay, depending primarily upon thehardware used, the degree of automation, the numbersof units handled and the types of battery terminals.A few common connection methods are as follows:

■ Wires and alligator clips (usually for largerbatteries)

■ Manual plug-in of flat tabs to forming strips(usually for small single cells/batteries)

■ Loading of trays that may contain 20-50 smallbatteries and insertion into formation bays using‘snap-on’ contacts or pressure springs.

Whatever the connection method, a few common areasof concern apply:

■ Are the battery terminals and formation contactsclean?

■ If a pressure contact is used, are any componentsfatigued so that spring pressure is not adequate?

■ Are the contact surface areas substantial so thatlocalized resistive heating and/or oxidationdoesn’t take place?

■ Are the battery terminals and formation contactsmade from low-resistance materials that will notproduce significant voltage drops? Are thesematerials easily corroded or oxidized?

These issues may seem trivial, but many formationconnectors have minimal contact areas with batteryterminals and the contacts and terminals are made frommaterials that are easily corroded by battery acid (steel,tin, copper) and/or are air oxidized at the hightemperatures generated at the contact points (copper,copper-bronze). The use of more rugged materials suchas nickel plating will minimize the above problems, butsuch materials may have significantly higher resistivities.High scrap levels or high formation recharge categorycan be created by the improper choice of connector


Formation equipment, battery monitoring and product testing

designs and/or materials and, more commonly, byinfrequent inspection and cleaning of formationequipment contacts.

The cleaning of battery connections is also a key healthand safety issue. Hydrogen and oxygen gases aregenerated during the formation process: a potentiallyexplosive mixture of gases is formed, which only needsa spark from a corroded connector to cause anexplosion or even a fire. This has the potential to causeinjury or death to personnel in the area: quite apart fromthe almost certain damage to batteries and/ orequipment.

Additional information about gas monitoring is given insection 13.3.

12.2 Formation Bay or CircuitConfigurationsThere are three approaches to how batteries areconfigured in formation circuits:

■ Series strings■ Series-parallel arrays■ Series-parallel matrices

By far the most common approach is to have a seriesstring of batteries charged by a single rectifier or powersupply. This is an effective approach and can result ingood finished battery uniformity if voltage drops due tohigh contact resistances are not an issue. The majordrawback is that one open contact (due to one openinternal battery connection or to poor or brokenformation bay mechanical contacts) can result in theloss of a whole string if not detected.

Series-parallel arrays are useful in that more batteriescan be formed from a single rectifier or power supply bydividing the available current (with all strings having thesame total voltage), but there is a danger of over-formation or even thermal runaway if one string, due toeven a slightly lower overall resistance, draws adisproportionate amount of the total formation currentavailable at the expense of the other strings. If this iseven a subtle effect there may be a significant variationin product quality string-to-string. This can be avoided inthe setup of the formation circuits by using “steeringdiodes” or other electronic measures to ensure thatroughly equal currents flow through each of theparalleled strings. If an “open” condition occurs in oneof the strings, however, it is lost as would be the case ina simple series-string arrangement; in addition, the totalcurrent available will now be distributed among theremaining strings according to their individual series

resistances. Thus, current would flow through theremaining strings, but at significantly higher levels thanplanned. If undetected by personnel or monitoringequipment, this would result in over-formation, andpossible destruction, of the remaining batteries.

The most effective approach, but also the mostcomplicated from a mechanical standpoint, is to useseries-parallel matrix connections where two or moreseries strings are put in parallel, but there are also cross-connections at some interval so that a matrix is created.This approach, along with the two previousconstructions, is shown in FigurFigurFigurFigurFigure 20.e 20.e 20.e 20.e 20. The majoradvantages of matrixing are that current is distributedmore uniformly and in the event of an “open” battery orcontact current continues to flow around the defectiveposition. Batteries immediately adjacent to the defectiveposition are affected to some extent (i.e., theyexperience somewhat higher formation current levels),but those further removed are not noticeably influencedwhen cross-connections are made between all units.The important point is that current continues to flowthrough all of the strings in a roughly equal fashion.Complete strings are not lost as in series-string andseries-parallel designs and whole strings are not heavilyovercharged in the event of an open battery. Matrixing is

Battery Connections For Series Strings, Series-ParallelArrays And Series-Parallel Matrixing.

Figure 20

A.Simple Series-String Battery Connections

B.Series-Parallel Array Connections

C.Series-Parallel Matrix Connections


usually done for single cells or small batteries wherelarge numbers of units are formed in individual bays.With these products, trays or carousels are used inwhich connections are made automatically so thatcross-connections can be done between each unit.This approach gives the most uniform currentdistribution and ensures that the effects of defectiveunits are minimal, but there is an added cost.


12.3 Critical Maintenance of FormationEquipmentTo obtain optimal results from formation equipmentfrequent maintenance is required. Some of thisinvolves electrical equipment such as rectifiers andDC power supplies, which must be calibrated on aregular schedule (this is essential for ISO 9000 or QS9000 certification). The quality of the incoming AC linepower should also be analyzed periodically. Computercontrol and monitoring equipment must similarly bemaintained and calibrated, but perhaps the mostcritical aspect of formation-room equipment is theactual hardware that accommodates the batteries andwhich may be exposed to the high temperatures andacid fumes and spray that go along with such closecontact.

One of the most important parts of maintaining aformation room is to carry out regularly scheduledabrasive or chemical cleaning of hardware used toconnect batteries in formation bays. Oxidized orcorroded contacts can contribute large voltage dropsto battery strings and this can cause undercharging orno charging at all in extreme cases. This can bedetected if current/voltage monitoring is done on allbattery strings, but if this is not done some batterieswill be taken off formation with low voltages or in a“dead” state (i.e., zero voltages) and it may beattributed to the batteries and not the connectors.Because of this, connector hardware must be cleanedregularly, often enough that oxide and corrosionbuildup cannot accumulate to levels that affectcontact resistances. If an automated monitoringsystem is not in place, poor contacts can be detectedmanually by taking voltage and current readings onindividual batteries or strings.

Cooling and heating equipment should also bemaintained effectively. If forced-air heating or coolingis used, CFM and temperature measurements shouldbe taken frequently in each of the formation bays toensure that airflows are correct. If water baths areused for cooling, water should be checked frequentlyfor temperature, flow rate (if applicable) and pH toensure that acid buildup is not severe.

All removable trays, racks, tables, etc. should bewashed and cleaned of acid frequently in order toextend life and to minimize the occurrence ofcosmetic rejects in batteries formed at later times(primarily terminal and label damage).

12.4 Power Quality and Equipment CostsAn important practical issue to consider is one ofpower quality and equipment cost and how these willimpact upon a specific VRLA product that is beingformed. Power quality varies greatly throughout theworld and in some areas it is very poor. High levels ofAC ripple and harmonics can and do feed directlyinto formation charging equipment; if filteringelectronics is not included in the formation rectifier orpower supply, large amounts of AC ripple will then besuperimposed upon the nominally DC charge profile.In formed batteries out in field service it has beenshown that AC ripple can result in severely-shortenedlifetimes by generating heating that results inaccelerated PAM softening and grid corrosion, asshown in FigurFigurFigurFigurFigure 21e 21e 21e 21e 21 [22]. Due to their low impedances,VRLA batteries are affected to a greater extent by ACripple than comparable flooded lead-acid productsbecause low ripple currents translate into higherripple voltages with the low impedances attributableto VRLA products.

AC ripple is a form of “mini-cycling” that can wear outa battery prematurely in service, but it can also havenegative effects in formation, depending upon itsamplitude, symmetry and frequency [23]. In additionto temperature effects and enhanced grid corrosion,ripple can reduce oxygen over voltage values therebyincreasing gassing during formation. Ripple is also



AC Ripple Voltage And Current Representation(Upper Figure) And Its Effect On Cell TemperatureAnd Cycle Lifetime.

Figure 21

Correlation of Battery Voltage and Charger Ripple Current

Test Battery is 8 Ah 12V SLA Type

Volts

Amps

Time (mSEC)

7.0

6.5

12

6

0

-6

-12

VCM

ICM

0 10 20 30 40 50 60 70

Ripple current (effective val.)Net CurrentItem Value 0.1C 0.2C 0.5C 0.8C 1.0C

TemperatureRise (ºC) 0.1 0.2 0.5 1.2 4.0 6.0

Proportionof life (%) 100 97 93 77 61 50

13. Battery Monitoring DuringFormationFormation system monitoring is essential for both qualityand safety reasons, as well as to keep scrap levelsminimal. Formation scrap is the most expensivebecause units that are scrapped here have themaximum input of materials and labor of any stage ofmanufacturing other than finishing. Therefore, it isimperative that some form of monitoring equipment beused, even if this is only a formation-room worker with amultimeter.

13.1 Electrical Monitoring

The outputs of the charging system must be monitoredfor compliance with values for voltage and current as setout in the manufacturing documentation. In addition,measurements may be taken to ensure good powerquality in terms of low levels of AC ripple and harmonicsreaching the batteries being formed. Continuousrecording of these data by Quality or Manufacturingpersonnel, with SPC charting posted in the formationarea, is highly recommended.

For the batteries themselves, the following parametersshould be monitored and analyzed (monitoring alone isnot enough: the data must be interpreted andappropriate action taken if necessary):

■ Initial currents (CV or TC charge) or voltages (CCcharge)

■ Top-of-charge (TOC) voltages (peak voltagetoward the end of a CC charge step, usually thelast one at the end of formation)

■ Finishing currents (CV or TC charge)■ Integrated ampere-hour input■ Presence of any timing kickouts and whether or

not they were properly re-initiated■ Overall voltage-time or current-time formation

profiles (sampling basis only)■ Discharge capacities if the formation algorithm

includes a discharge

not always symmetrically-imposed on the DC signaland so there can be a net increase or decrease in thetotal charge applied (i.e., greater or lesser Ahformation inputs, respectively) depending uponwhether it is skewed to the charge or discharge side.Given all of the above, it is highly recommended thatformation power supplies be provided with the properfiltering equipment (capacitors and chokes) so thatminimal AC ripple is fed to the forming VRLAbatteries. It should be noted that the chargingequipment available from Digatron/ Firing Circuitsprovides inductive filtering to minimize ripple current.



Initial currents or voltages are important because theyindicate whether or not the initial current flow is at theprescribed level and that most or all of it is going into theformation process (conversion of lead sulfate to theactive materials) and not into gassing because of highresistances. Low currents on CV or TC charge orabnormally high voltages on CC charge indicate thatsome or all of the unformed units are heavily sulfatedand/or there may be connector/terminal problems (highresistances). Even though current is flowing thedistribution between strings may not be uniform and iftimed formation algorithms are used without currentintegration this will result in low Ah inputs to thebatteries. Electrical energy that goes into resistiveheating or gassing will, obviously, not count towardforming the active materials but it will be included in thetotal formation Ah input.

Careful voltage monitoring during CC formationalgorithms is useful as a feedback tool for triggering restor discharge steps and for defining product quality; aswith the other parameters discussed, TOC “windows”are defined for manufactured products and these valuesare used for accept/reject purposes. When voltages arelow (when they should be high), this indicates that thebatteries are being under formed; if voltages are in thegassing region (above ~2.35 V/cell) for appreciableperiods of time weight losses and, possibly, gridcorrosion will be high, battery internal temperatures willbe elevated and dangerous over-formation of thepositive plate is possible. If TOC voltages are unusuallyhigh (as they would be for a flooded lead-acid product),it indicates complete saturation of the plate stacks,which may not be desired for some products formedsealed with ~95% saturation levels. (This depends onwhether the batteries are formed “open” or “sealed”, seesections 3.3.1 and 7.1). While it is often not possible tomonitor every battery, compliance of the overall voltage-time or current-time profiles with manufacturing standardcurves should be ensured. Non-compliance canindicate problems with either the formation equipment orthe filled batteries going into formation or both.

It is also important to monitor finishing currents duringCV or TC charging, as they can indicate rectifier orpower supply charging voltages being set too high orone or more strings in a series-parallel array being open.High finishing currents can also indicate that batteriesare too hot or they have low saturation levels and, thus,high levels of oxygen recombination. In the extreme,high finishing currents can be a precursor to a part ofthe formation bay going into thermal runaway.

For CV and TC charging, integration of ampere-hourinputs is necessary to ensure that the proper amount offormation current is being applied; for CC charging,monitoring of the applied current level and the steptimes is sufficient to determine accurately the Ah inputs.

A serious practical problem in many formation systemsis proper re-initiation of the formation profile following anunscheduled power interruption. Ideally, the electricalsystem should pick up exactly where it left off but evenwhen this is done the forming batteries will haveexperienced an unscheduled “rest” of some duration (oreven two or more). If interruptions occur early information the effect is probably minimal but duringovercharge the liquid diffusion and gassing processeswill be significantly affected. If it occurs within the firsthour or so, the formation schedule can simply be re-initiated. If it occurs in the last hour or so, earlytermination will probably not affect product qualityseverely. The bigger problems are if and when theyoccur in the middle of the formation, if they are extensiveand if there are multiple outages. For manuallycontrolled formation this can create confusion anderrors. For computer-controlled systems properprogramming can account for outages, but in any eventthe overall manufacturing schedule will be disrupted.However, if there is no compensation for outages theuniformity of product quality will be greatly affected, aseach group of formed batteries may have widelydifferent Ah inputs.

If one or more discharges are part of the formationalgorithm their duration and Ah output can be used asan indicator of the quality of the formed batteries;beyond this, the values can be used in matching VRLAbatteries into larger arrays. In matching of modules tomake higher-voltage (series) and ampere-hour (parallel)batteries it is a reliable rule-of-thumb that matching oflike-capacity modules is of paramount importance –more so than the nominal capacity. Thus, high- and low-capacity modules must be matched with comparablepartners rather than having them mixed. A batterycomprised of all low-capacity modules will give betterinitial performance than one comprised of a mixture ofhigh- and low-capacity units. Obviously, the bestperformance is obtained when all high-capacitymodules are matched.



13.2 Temperature MonitoringTemperature monitoring of the formation roomenvironment, some of the formation equipment and thebatteries themselves is important. VRLA batteries arevery sensitive to the formation temperature, so if aformation room is being used without active heating orcooling (forced air, water) it is imperative thattemperature be monitored at a number of independentpositions throughout the room to ensure that a nominalformation temperature exists and that it is relativelyuniform within a range of, at most, several degreesCentigrade. If the formation-room temperature is toohigh the batteries will be over-formed or, in the extreme,can go into thermal runaway. This will result in highgassing levels and weight losses, possibly high levels ofgrid corrosion and poor positive-plate quality. If theambient temperature is too low under-formation canresult, with low initial discharge capacities (particularlythe positive plate) and high levels of unformed oxides(resulting in poor shelf life). In some VRLA products, ifthe initial formation is done at too-low temperatures it isdifficult or impossible to effectively recharge thebatteries following formation; the reason for this is notknown. Both the nominal temperature for the formationroom and consistency throughout the year areimportant, particularly if the manufacturing plant is notheated and air-conditioned. The worst condition is tosimply form batteries on tables in a plant withouttemperature regulation of any type; this will result invariable product quality throughout the year and it islikely that batteries produced during either the summeror winter (or both) will be of inferior quality.

It should be noted that critical formation equipment suchas rectifiers, power supplies, power resistors, monitoringequipment and control computers must be located in acompletely separate room from the formation room itself.The high temperatures and acidic atmosphere in theformation room can damage delicate electronicequipment and shorten their lifetimes considerably.

As noted earlier (section 7.3) as a general rule smallVRLA batteries (~25Ah or less) may form better if heatedand larger batteries require cooling for optimalformation. In either case, appropriate regulation of thetemperature immediately around the batteries (asopposed to the formation room ambient temperature) willresult in superior and consistent product quality. Thus,temperature monitoring of forced air or still or circulatedwater used to heat or cool batteries, respectively, is alsorecommended.

If monitoring of air or water is done as described abovethen monitoring of battery surface temperatures is notnecessary, as the temperature differences will be quitesmall. However, in cases where no active cooling orheating is applied (e.g., bench formation with notreatment) it is a good idea to monitor battery skintemperatures (selected batteries on a sampling basis,particularly center batteries in large groupings) in orderto correlate this information with the formation algorithmtiming and to ensure that batteries do not overheat orform too cold.

13.3 Gas MonitoringIn the later stages of formation, the forming batteriesgive off various gases, particularly when they are formedopen. Early in formation, the positive plate goes intoovercharge, generating significant amounts of oxygengas. Vented oxygen poses no particular problems information rooms. Later, when negative plates go intoovercharge hydrogen gas is given off. This is also not aproblem unless it reaches a level of at least 4% bypartial pressure; at this point and above it forms anexplosive mixture with air in the presence of a sparksource (which are usually abundantly present information environments). Other gases that are routinelygenerated during formation are carbon monoxide andcarbon dioxide. In cases where battery internaltemperatures reach levels of 160-190oC (this normallyonly occurs in a thermal-runaway situation), hydrogensulfide can be generated on negative plates duringheavy overcharge. Hydrogen sulfide is extremely toxic tohumans, even at very low concentrations. Moreover, itattacks any copper or copper-coated electricalcomponents and forms an insulating surface coating ofcopper sulfide, rendering the devices useless.

While it is unusual in practice to have significantamounts of hydrogen sulfide generated, it isrecommended that several types of gas monitors beinstalled in manufacturing formation rooms. At the veryleast, hydrogen monitoring should be employed forsafety purposes. Monitors should be placed at locationsin the formation room where hydrogen gas can begenerated in large amounts or where it may accumulate.Clearly, this also calls for adequate air movement andventilation to ensure that hydrogen gas buildup does notoccur in pockets that may explode. Carbon dioxide andcarbon monoxide are not likely to be generated in largequantities but CO monitors are common andinexpensive and it takes little investment to installseveral of these in a formation room.



Perhaps the most serious concern from a safety andequipment standpoint is the potential buildup ofhydrogen sulfide, which is generated when VRLAbatteries are seriously overheated during overcharge.Incidents are documented where telecom and UPSinstallations have been destroyed by VRLA batteries thatgenerated large quantities of hydrogen sulfide on floatwhen the systems went into thermal runaway [24].Human toxicity is likewise severe, so it is highlyrecommended that hydrogen sulfide monitoring be apart of any VRLA manufacturing formation room.

In most manufacturing operations, batteries in formationwill occasionally explode, or “pop”, due to hydrogenbeing present internally during overcharge and a sparkbeing created from a poor COS or squeeze weldcontact. Such a defective connection will conductcurrent but at some point an arcing condition may occur.If hydrogen gas within the battery ignites there may beenough force to rupture the plastic case, creating plastic“shrapnel” near the battery. Clearly, this is a hazard foremployees and by itself makes the wearing of safetyglasses or, better, face shields mandatory. Thefrequency of this “popping” can be used as a qualityindicator for the upstream cast-on-strap and/or through-the-wall squeeze welding operations; if they occurfrequently the welding equipment and proceduresshould be carefully inspected.

14. Post-Formation Handling andIn-Line Product TestingWhen formation is completed, batteries are notnecessarily ready for shipment immediately, althoughsome manufacturers with very strong confidence inproduct quality (no doubt backed up by extensivesampling of formed batteries over a long period of time)do ship directly after formation. For most manufacturers,however, batteries from formation are subjected to thefollowing general processes:

■ Batteries are cleaned of any excess acid andinspected for physical case damage and possiblecorrosive attack on terminal posts or labels. Anybatteries that clearly have leaks in seal areas (lid/box, terminal posts) must be scrapped.

■ Batteries immediately after formation will have veryhigh open-circuit voltages (OCVs) due to trappedgas and excess surface charge on the plates.However, OCV readings directly after formation willidentify dead batteries (to be scrapped) and thosewith low, but significant, voltages (to be

recharged). Multicell batteries which clearly haveone or more dead cells (e.g., a 12V battery with anOCV of ~10V or 8V) should also be identified andscrapped. OCV monitoring directly after formationmay not be feasible for single cells or smallbatteries, but for larger monoblocks it is useful inremoving scrap batteries and thus minimizingfuture wasteful handling and storage.

■ For batteries formed open, completion ofassembly is done at this stage. This may involvesimply mounting one or more vent valves andcaps and/or it may require heat sealing, gluing orultrasonic welding of an outer cover. In any case,areas of the battery involving these operationsmust be dry and completely free of acid.

■ Batteries are then put into a stable environment,possibly temperature-controlled, for several daysuntil their electrical characteristics have stabilizedand they can be sorted for future disposition.

14.1 Visual StandardsMany VRLA companies have a formal set of visualstandards for manufacturing personnel to use inevaluating batteries for shipment following formation.Sample criteria that may be used for sorting are asfollows:

■ CategorCategorCategorCategorCategory 1.y 1.y 1.y 1.y 1. Batteries with only minor defects thatcan be cleaned up and are acceptable after suchtreatment.

■ CategorCategorCategorCategorCategory 2.y 2.y 2.y 2.y 2. Batteries with cosmetic defects thatwill not affect performance and are acceptableelectrically can be used in closed-caseapplications.

■ CategorCategorCategorCategorCategory 3.y 3.y 3.y 3.y 3. Batteries with major cosmetic damagebut acceptable electrical performance can bereworked, if feasible.

■ CategorCategorCategorCategorCategory 4. y 4. y 4. y 4. y 4. Batteries with major cosmetic damagethat may impact performance and/or lifetime mustbe scrapped.

Each product must be evaluated and a series of visualstandards covering all of the problems seen in post-formation batteries must be developed to put batteries inone of the above four categories. Examples of commonproblems included in the above categories are: case/label acid damage, poor seals/acid leakage, bulged orcracked cases, corroded terminals, improperly appliedlabels and deep scratches or dents.



14.2 In-Line Product TestingFollowing cleaning and inspection after formation andstorage for several days, batteries are then put througha series of tests in order to determine product qualityand segregate them into several categories for furtherhandling. The primary tool used is OCV measurement,but in some processes AC impedance and high-ratedischarge performance are also measured. It must bestressed that all of these parameters change with timeoff formation, so in assessing product quality charts withlistings of daily parameter levels should be employed(see below).

14.2.1 Open-Cir14.2.1 Open-Cir14.2.1 Open-Cir14.2.1 Open-Cir14.2.1 Open-Circuit Vcuit Vcuit Vcuit Vcuit Voltage Measuroltage Measuroltage Measuroltage Measuroltage Measurementementementementement

OCV values tend to drop on a daily basis by a fewmillivolts per cell depending upon the product type, thefinished electrolyte strength and the effectiveness offormation. In addition, batteries with higher voltagesafter formation show a slower decrease in OCV valuesthan those with lower (but acceptable) post-formationvoltages. All batteries have a relatively steep drop inOCV over the first couple of weeks and this then“flattens out” to a lower rate. In addition, the rate ofdecrease in OCV is a function of temperature, so it isimperative that storage and measurement be done at acontrolled temperature level, within a window of 3-4oC atmost. Typical self-discharge curves for VRLA single cellsare shown in FigurFigurFigurFigurFigure 22;e 22;e 22;e 22;e 22; multiples apply for multi-cellbatteries.

OCV measurements are usually not simply a “pass/fail”affair, as batteries are often sorted into a number ofcategories, among these being (in order of increasingOCV):

■ Dead, low voltage (e.g., <2.000V) or reverse-polarity (all are reject category)

■ Recharge category■ Low acceptable or high acceptable (to be

subjected to further test and, if acceptable,shipping to customers)

■ High-voltage (reject category)

Dead batteries have either an internal open connection(COS, intercell weld) or they were not properlyconnected to the formation system during charge.Reverse-polarity batteries were formed in reverse and,thus, positives were formed as negatives and vice-versa; both are scrap. Low-voltage batteries also mayhave had a poor connection in formation or they mayhave a near-fatal internal problem such as an incipient

short circuit, or low fill weight; in any event, it isconsidered too dangerous and wasteful to attempt torecover these batteries and they are also scrapped.

“Recharge category” batteries have low OCV values,but they are considered to be possibly recoverable asacceptable product. They are incompletely formed forsome reason and often have relatively high internalimpedances due to sulphation. Because of this they areoften recharged in groups using high-voltage (3.5-4.0 V/cell or more) constant-current charging for some periodof time, after which they are subjected to the same in-line test criteria as for the original formation. Somemanufacturers will use their formation equipment forrecharging, using a short, modified algorithm. In somemanufacturing processes a second recharge treatmentis allowed, but it should be recognized that with each

Typical Self-Discharge Curves For VRLA Batteries.

Figure 22

% N

omin

al C

apac

ity A

vaila

ble

B.Self-Discharge Curves At Different Storage TemperaturesOp

en-C

ircui

t Vol

tage

, V

Time on Stand, Months

2.2

2.15

2.1

2.05

2

1.95

1.9

1.85

1.80 5 10 15 20 25

10 20 30 40 50 60 70 80

100908070605040302010

0

Months of Storage from Full Charge

A.Self-Discharge Curves for One- and Two-year Shelf Lives

40ºC20ºC

10ºC

0ºC


follow-up charge treatment it becomes much more likelythat these batteries contain some type of defect thatmay show up early in field service. Recharging,particularly multiple times, has the distinct drawbackthat, if effective, it can mask these subtle defects (suchas small leaks, hydration shorts, etc) so that defectiveproduct is shipped. Manufacturers must be very carefulin setting recharge procedures and standards foracceptance, as too-generous guidelines can and willresult in higher levels of customer dissatisfaction andreturns.

The vast majority of batteries should normally be in the“acceptable” categories. If a company’s batteries go intogeneral use there may be only a single voltage windowfor product to be shipped immediately. However, if someof a company’s markets involve the application of high-voltage systems or have high-performance requirementsthere may be two (or more) “acceptable” categories,one (A-group) being superior in terms of OCV to theother (B-group).

In general, higher post-formation OCVs (A category asopposed to B) indicate a better-formed product and,thus, one with longer shelf life and superior electricalperformance. However, some batteries can be and areover-formed (high-voltage, or HV, rejects), resulting intoo-high weight losses and possible internal damage(enhanced grid corrosion, low saturation levels, over-formed PAM, too-high electrolyte specific gravity).Clearly, if the formation process involves adjustment ofelectrolyte volumes after formation this type of defect isnot as likely to be detected. For batteries formed in asealed state this is particularly pertinent. In addition topossible internal damage, voltages may be so high forthese batteries that they will tend to be undercharged inapplications where they are mixed with “normal OCV”batteries in high-voltage strings. This will be particularlytrue in some float applications; in others, their highvoltages may cause undercharging of the “normal”batteries and, in extreme cases, partial discharge.

An example of a chart used in sorting batteries afterformation is given in Table 3; this same Table can beused for sorting batteries after recharge or a short boostcharge of any type. Obviously, any charging process willbe the “zero point” for the chart, with “days off form”really reading as “days off charge”, whatever the typeand duration of charge.

14.2.2 AC Impedance Measur14.2.2 AC Impedance Measur14.2.2 AC Impedance Measur14.2.2 AC Impedance Measur14.2.2 AC Impedance Measurementsementsementsementsements

In addition to OCV, the measurement of AC impedancesof batteries can be a valuable sorting tool. Here, it isusually the case that a “pass/fail” value is used for eachproduct, as batteries of different designs, voltages andAh capacities will have different nominal impedancevalues. In batteries, single-cell impedances are additivedepending upon the number of series-connected cells.Larger batteries (in terms of Ah capacity) and those withthinner plates have relatively lower impedances, as thisparameter is a function of plate surface area and platespacing. Typical impedance readings for a number ofdifferent VRLA single-cell and 12V products are given inTable 2. These are all thin-plate products (thicknesses of~1.2mm or less) and so the AC impedance values willbe lower than for comparable (in terms of voltage andAh ratings) thicker-plate batteries.

AC impedance is also a function of the state-of-healthfor a given VRLA product type and is an indicator of thequality of the materials and processes in use. The higherthe impedance reading the poorer the battery quality(relative to the nominal value for that specific product).Thus, the nominal acceptable impedance reading is anallowable maximum value, with batteries above thatvalue being sorted out for recharging (moderately high)or as scrap (very high). It should be noted that it ispossible for VRLA batteries to have acceptable OCVvalues but unacceptably high impedance readings, asthese two parameters have little in common electrically.

There is no acceptable minimum value for impedancebecause it can never be “too low.” In practice, the lowerthe impedance the better the battery quality. Thus,average impedance readings for production batches ofbatteries are an indicator of the effectiveness of themanufacturing process and should be used by Qualityand Manufacturing personnel as such. AC impedancevalues are usually taken at 1 kHz with a Hewlett-PackardModel 4328A meter or an equivalent instrument. As thisinvolves a four-point measurement using delicate probesit is necessary to use great care and reproducibility intaking measurements on batteries, as simply varying thelocation of the probes on the battery terminals or appliedmeasuring probe pressure can result in significantvariances in measured values. It should be noted thatAC impedance is a “no-load” test, so it says nothingabout the capability of a battery to sustain certaindischarge currents and/or the integrity of the internalbattery connections. For this, an additional test isneeded.



14.2.3 High-Rate Discharge Measur14.2.3 High-Rate Discharge Measur14.2.3 High-Rate Discharge Measur14.2.3 High-Rate Discharge Measur14.2.3 High-Rate Discharge Measurementsementsementsementsements

In addition to OCV and (possibly) AC impedance, somemanufacturers also carry out a short-duration high-ratedischarge test, usually at about the 10C discharge rateat room temperature. As this is not a completedischarge, variations in ambient conditions are not ascritical as they would be for determining full capacities.The discharge time is for ~5-10 seconds, so a rechargeis not necessary. This is a useful test, as it not onlydefines finished-product electrical quality but it also actsas a check on the integrity of the internal batterymechanical connections.

It is often set up as only a “pass/fail” test, using aminimum voltage threshold at 5 or 10 seconds; anybatteries whose voltages are at or above this voltage areaccepted; those slightly below it may be put into an“acceptable but inferior” category for use in certain non-critical low-rate discharge applications; alternately, theymay be sent back for recharge. In practice, it can alsobe used as a test to sort nominally acceptable batteries(i.e., those whose voltages are above the thresholdvalue) into “normal” and “superior” categories,particularly for use in high-rate discharge applicationssuch as engine start or UPS.

This type of testing is somewhat subjective, as itdepends upon the shapes of the discharge and voltagerebound curves, as shown in Figur Figur Figur Figur Figure 23.e 23.e 23.e 23.e 23. Withprogrammable testers, collection of data and analysis,even on such a detailed level, is not only possible butalso commonplace.

FigurFigurFigurFigurFigure 23a e 23a e 23a e 23a e 23a shows a typical discharge and reboundcurve for a strong battery, one with outstanding porestructures in the plates and good diffusion kinetics. Ondischarge, the coup de fouet (initial, instantaneousvoltage drop) is followed by strong voltage recovery andan increasing voltage at the 5-second point, indicative ofgood electrolyte diffusion into the plate pores to supportthe high discharge current. Following termination of thedischarge the voltage recovery is sharp, againsuggesting effective diffusion kinetics. FigurFigurFigurFigurFigure 23be 23be 23be 23be 23b is anexample of the discharge and voltage recovery curve foran inferior battery. During the discharge the voltage isnot strong and may even begin to drop off toward theend of the 5-second duration. The recovery is gradual,indicating restricted diffusion of acid from the separatorreservoir into the plate pores. Such a battery will not bea strong performer in high-rate applications.


While post-formation testing and evaluation are nottechnically a part of the formation process, it is hopedthat the foregoing will illustrate the necessity and powerof this stage of manufacturing in validating theeffectiveness of formation or catching and correcting itsshortcomings. In some cases, it can also providevaluable information on processes earlier in themanufacturing stream (plate quality, COS integrity, heat-seal effectiveness, etc.) This is an area that is oftenoverlooked or given short shrift, but it is one that willhave a major impact on the quality and uniformity ofproduct reaching the end user.

High-Rate Discharge Voltage/Time Curves ForAcceptable And Unacceptable Battery PerformanceOn A 5-Second Test.

Figure 23

A.Discharge/Rebound Curve Typical for a "Strong" Battery

Test

Vol

tage

Discharge/Rebound time, Seconds

DischargeInitiated

DischargeKickout

Note the strong voltage during discharge andthe sharp voltage rebound after kickout.

Test

Vol

tage

Discharge/Rebound time, Seconds

Note the weak voltage during discharge andthe sluggish voltage rebound after kickout.

B.Discharge/Rebound Curve Typical for a "Weak" Battery

DischargeInitiated

DischargeKickout


Troubleshooting formation problems

15. Jar Formation Toubleshooting:Problems And Solutions

15.1 Filling and Fill-to-Form1. Batteries overheat following acid filling1. Batteries overheat following acid filling1. Batteries overheat following acid filling1. Batteries overheat following acid filling1. Batteries overheat following acid filling

a. Chill unfilled batteries to –30oC (Caution: this processis energy intensive and the low temperature maycause damage to seal areas, and the battery casemay be susceptible to cracking during handling)

b.Chill electrolyte to –10oCc. Immerse filled batteries in chilled water bathd.Slow down filling speed

2. Separator above plates is damaged during2. Separator above plates is damaged during2. Separator above plates is damaged during2. Separator above plates is damaged during2. Separator above plates is damaged duringaaaaacid additioncid additioncid additioncid additioncid addition

a. Slow down fill speedb.Use acid-diffuser nozzle design

3. Lead sulfate hydration shor3. Lead sulfate hydration shor3. Lead sulfate hydration shor3. Lead sulfate hydration shor3. Lead sulfate hydration shorts forts forts forts forts form in them in them in them in them in theglglglglglass-mat separatorass-mat separatorass-mat separatorass-mat separatorass-mat separator

a. Use sodium sulfate in electrolyteb.Use slower filling to yield more uniform acid

distributionc. Keep temperature down during the fill-to-form time.d.As a last resort, put batteries onto formation

immediately after fill

4. Conversion of PbSO4. Conversion of PbSO4. Conversion of PbSO4. Conversion of PbSO4. Conversion of PbSO44444 to PbO to PbO to PbO to PbO to PbO22222 is poor is poor is poor is poor is poora. Increase fill-to-form time

5. Batteries r5. Batteries r5. Batteries r5. Batteries r5. Batteries regurgitate acid after fillingegurgitate acid after fillingegurgitate acid after fillingegurgitate acid after fillingegurgitate acid after fillinga. Use cooling bath after fillingb.Check dried plates for excessive carbonation

15.2 Pre-Formation Conditions1. Batteries ar1. Batteries ar1. Batteries ar1. Batteries ar1. Batteries are too hote too hote too hote too hote too hot

a. Allow longer fill-to-form timeb.Use chilled water cooling between fill and formationc. Use a low-current initial charge for 1-2 hoursd.Reduce cooling efficiency during fill, fill-to-form;

extend filling and fill-to-form times

2. Batteries ar2. Batteries ar2. Batteries ar2. Batteries ar2. Batteries are re re re re regurgitating acidegurgitating acidegurgitating acidegurgitating acidegurgitating acida Form open instead of sealedb.Use external “acid tower” fitted to the fill port to take

up expelled acidc. Modify cure/dry conditions to minimize plate

carbonationd.Process batteries rapidly after cure and dry, minimize

time on floor before fill and formation

3. Loading of for3. Loading of for3. Loading of for3. Loading of for3. Loading of formation bays takes too much time,mation bays takes too much time,mation bays takes too much time,mation bays takes too much time,mation bays takes too much time,fffffill-to-forill-to-forill-to-forill-to-forill-to-form time is high and variablem time is high and variablem time is high and variablem time is high and variablem time is high and variable

a. Use multiple acid fillers to speed up loading of baysb.Use smaller numbers of batteries on the formation

circuits

4. Electrical continuity check shows an “open” r4. Electrical continuity check shows an “open” r4. Electrical continuity check shows an “open” r4. Electrical continuity check shows an “open” r4. Electrical continuity check shows an “open” readingeadingeadingeadingeadingooooon a string or cirn a string or cirn a string or cirn a string or cirn a string or circuitcuitcuitcuitcuit

a. Carefully inspect connectors for corrosion or oxidationb. Inspect connectors for broken wiresc. Inspect wires coming from rectifiers/power suppliesd.Measure individual batteries for “open” resistance

readings (with and without connectors attached)

15.3 Formation Process1. Batteries ar1. Batteries ar1. Batteries ar1. Batteries ar1. Batteries are too hot during fore too hot during fore too hot during fore too hot during fore too hot during formationmationmationmationmation

a. Increase airflow or water circulation rate, decreasecooling water temperature

b.Reduce ambient temperature conditionsc. Reduce current levels, extend formation timed.Put in rest periods to dissipate heate. Provide more space between batteriesf. Lengthen fill-to-form time, reduce initial battery

temperatureg.Shorten time for high initial current charge, if usedh. Change plate materials, use red lead in positive paste,

carbon in negative pastei. Use sodium sulfate in electrolytej. Shorten fill-to-form time to reduce sulfation level, lower

battery resistancek. Some parallel strings receive too much currentl. Use pulsed-current algorithm

2. Batteries ar2. Batteries ar2. Batteries ar2. Batteries ar2. Batteries are too cold during fore too cold during fore too cold during fore too cold during fore too cold during formationmationmationmationmationa. Increase airflow rate, air temperatureb. Increase cooling water temperature, slow circulation ratec. Increase ambient temperatured. Increase charge current, shorten formation timee. Some parallel strings receive too little current

3. For3. For3. For3. For3. Formation ampermation ampermation ampermation ampermation ampere-hour input is too lowe-hour input is too lowe-hour input is too lowe-hour input is too lowe-hour input is too lowa. Check for power outages during the formation period

(did the formation programmer compensate?)b.Check rectifier/power supply setting - too low?c. Ambient temperature too low for CV or TC formation

algorithmsd.Cooling air or water too colde. Check formation programmer for the correct formation

algorithmf. Batteries heavily sulfated, current-time profile is low

(CV or TC)g.Batteries under filled, resistances are high, current-

time profile is lowh. Connector hardware is corroded, oxidizedi. Battery terminals are corroded, oxidized



4. For4. For4. For4. For4. Formation ampermation ampermation ampermation ampermation ampere-hour input is too highe-hour input is too highe-hour input is too highe-hour input is too highe-hour input is too higha. Check controller for correct algorithm current/voltage

settings, timingb.Too-high rectifier/power supply settingc. Ambient temperature too high for CV, TC formation

algorithmsd.Cooling/heating air/water too warme. Interrupted formation reinitiates from the beginning

5. End-of-charge curr5. End-of-charge curr5. End-of-charge curr5. End-of-charge curr5. End-of-charge currents arents arents arents arents are too high in CV ore too high in CV ore too high in CV ore too high in CV ore too high in CV orTTTTTC forC forC forC forC formationmationmationmationmation

a. Batteries are too hot due to poor temperature regulationb.Rectifier/power supply voltage too highc. Low fill weights in one or more cells and/or high

formation weight losses results in high O2-recombination level

d. Impurities lower oxygen over potential on positive,increase recombination current

e. Non-uniform distribution of current in a series-parallelstring formation bay

6. End-of-charge voltages ar6. End-of-charge voltages ar6. End-of-charge voltages ar6. End-of-charge voltages ar6. End-of-charge voltages are too high in CC fore too high in CC fore too high in CC fore too high in CC fore too high in CC formationmationmationmationmationa. Batteries are flooded, no oxygen recombination

taking placeb.Too much electrolyte in negative-plate pores, acts like

flooded batteryc. End-of-charge current higher than the programmed level

7. End-of-charge voltages (EOCV) ar7. End-of-charge voltages (EOCV) ar7. End-of-charge voltages (EOCV) ar7. End-of-charge voltages (EOCV) ar7. End-of-charge voltages (EOCV) are too low in CCe too low in CCe too low in CCe too low in CCe too low in CCforforforforformationmationmationmationmation

a. Low fill weights in some cells and/or high formationweight losses create too much void space, thereforetoo much oxygen recombination, lowers EOCV

b.Too little electrolyte in negative-plate pores, too muchrecombination

c. High impurity levels reduce hydrogen over potential atthe negative and/or the oxygen over potential at thepositive

d.Batteries are too hot, O2-reduction current increases,lowers EOCV

e. End-of-charge CC current is lower than theprogrammed level

8. Batteries r8. Batteries r8. Batteries r8. Batteries r8. Batteries regurgitating acid, acid spray occursegurgitating acid, acid spray occursegurgitating acid, acid spray occursegurgitating acid, acid spray occursegurgitating acid, acid spray occursa. Batteries too hot going into formationb.Batteries are too hot for the reasons given in Section 1

abovec. Heavy, deep carbonation continues to generate CO2

from platesd. Voltages and/or currents are too high, gassing is excessivee. Attach acid tower to fill port to catch regurgitated acidf. Use all-glass separator, higher surface area separator,

higher stack compression to hold electrolyte moretightly

g.Battery headspace is inadequateh. Batteries are overfilled and/or void space is too low

(high paste/grid weights)i. Equip formation room with sulfuric acid mist monitoring,

alarms

9. T9. T9. T9. T9. Toxic, explosive gases aroxic, explosive gases aroxic, explosive gases aroxic, explosive gases aroxic, explosive gases are generated in largee generated in largee generated in largee generated in largee generated in largeamounts, alaramounts, alaramounts, alaramounts, alaramounts, alarms soundms soundms soundms soundms sound

a. Too much overcharge ampere-hours on the negative,high hydrogen levels

b.Ventilation equipment inoperative, malfunctioning orunder-designed

c. Some formation bays have batteries in thermalrunaway, hydrogen sulfide is being generated –evacuate and shut down affected bays!

10. Batteries explode during for10. Batteries explode during for10. Batteries explode during for10. Batteries explode during for10. Batteries explode during formation, may causemation, may causemation, may causemation, may causemation, may causeplasplasplasplasplastic “shrapnel”tic “shrapnel”tic “shrapnel”tic “shrapnel”tic “shrapnel”

a. Poor internal battery connections cause sparks duringovercharge, H2 ignites, and cases are distorted orruptured

11. Batteries explode during for11. Batteries explode during for11. Batteries explode during for11. Batteries explode during for11. Batteries explode during formation, catch firmation, catch firmation, catch firmation, catch firmation, catch fireeeeea. Use flame-retardant case/lid materialsb.Equip formation room with sprinklers, smoke detectors

15.4 Post-Formation Handling and VisualInspection1. Acid and/or water damage to batteries1. Acid and/or water damage to batteries1. Acid and/or water damage to batteries1. Acid and/or water damage to batteries1. Acid and/or water damage to batteries

a. Apply measures as in Section 16.3, Section 5 to avoidfuture acid damage

b. Clean and dry battery thoroughly, examine terminals,labels for damage and scrap if severe

2. Acid damage to for2. Acid damage to for2. Acid damage to for2. Acid damage to for2. Acid damage to formation harmation harmation harmation harmation hardwardwardwardwardwareeeeea. Clean thoroughly before re-useb. Replace steel, copper connectors if damage is severe

3. Oxidation damage to for3. Oxidation damage to for3. Oxidation damage to for3. Oxidation damage to for3. Oxidation damage to formation harmation harmation harmation harmation hardwardwardwardwardwareeeeea. Clean thoroughly before re-useb.Replace if damage is severe

4. Exposed steel par4. Exposed steel par4. Exposed steel par4. Exposed steel par4. Exposed steel parts arts arts arts arts are rustede rustede rustede rustede rusteda. Clean with abrasive if minor

5. T5. T5. T5. T5. Terererererminal plating is corrminal plating is corrminal plating is corrminal plating is corrminal plating is corroded or buroded or buroded or buroded or buroded or burned away by acidned away by acidned away by acidned away by acidned away by acidor shoror shoror shoror shoror shorting, rting, rting, rting, rting, respectivelyespectivelyespectivelyespectivelyespectively

a. Scrap battery if severe; if minor use in closed-caseapplications

6. T6. T6. T6. T6. Terererererminal posts arminal posts arminal posts arminal posts arminal posts are bure bure bure bure burnished or parnished or parnished or parnished or parnished or partially melted duetially melted duetially melted duetially melted duetially melted dueto dead shorto dead shorto dead shorto dead shorto dead shorttttt

a. Scrap battery

7. Minor scratches and/or dents to batter7. Minor scratches and/or dents to batter7. Minor scratches and/or dents to batter7. Minor scratches and/or dents to batter7. Minor scratches and/or dents to battery casey casey casey casey casea. Rework and use as normalb.Train formation room personnel in better handling

techniques

8. Major dent or cracked/chipped case that may8. Major dent or cracked/chipped case that may8. Major dent or cracked/chipped case that may8. Major dent or cracked/chipped case that may8. Major dent or cracked/chipped case that mayindicate interindicate interindicate interindicate interindicate internal damagenal damagenal damagenal damagenal damage

a. Scrap battery



9. Acid leakage evident fr9. Acid leakage evident fr9. Acid leakage evident fr9. Acid leakage evident fr9. Acid leakage evident from lid/box seal, vent- valveom lid/box seal, vent- valveom lid/box seal, vent- valveom lid/box seal, vent- valveom lid/box seal, vent- valvearararararea or terea or terea or terea or terea or terminal post seal arminal post seal arminal post seal arminal post seal arminal post seal area.ea.ea.ea.ea.

a. Lid/box seal area – scrap battery or rework forclosed-case use

b.Terminal post seal area – see belowc. Vent-valve area – clean and dry

10. T10. T10. T10. T10. Top and/or sides of batterop and/or sides of batterop and/or sides of batterop and/or sides of batterop and/or sides of battery ary ary ary ary are bulged visuallye bulged visuallye bulged visuallye bulged visuallye bulged visuallyor to touchor to touchor to touchor to touchor to touch

a. If minor, hold for evaluation; if major, scrap battery

11. Dir11. Dir11. Dir11. Dir11. Dirt, oil and/or grt, oil and/or grt, oil and/or grt, oil and/or grt, oil and/or grease contaminationease contaminationease contaminationease contaminationease contaminationa. Clean thoroughly and use

12. Acid ar12. Acid ar12. Acid ar12. Acid ar12. Acid around teround teround teround teround terminal post(s) (may be simple acidminal post(s) (may be simple acidminal post(s) (may be simple acidminal post(s) (may be simple acidminal post(s) (may be simple acidcontamination during forcontamination during forcontamination during forcontamination during forcontamination during formation or a defective post seal)mation or a defective post seal)mation or a defective post seal)mation or a defective post seal)mation or a defective post seal)

a. Clean away acid and put battery on a 2- or 3-hourovercharge

b. If no leakage, accept as good product; if leakageoccurs during overcharge, scrap battery

15.5 Post-Formation Electrical Evaluation -OCV, Impedance, High-Rate Discharge.1. Batter1. Batter1. Batter1. Batter1. Battery is dead – zery is dead – zery is dead – zery is dead – zery is dead – zero voltageo voltageo voltageo voltageo voltage

a. Internal “open” connection in batteryb.No fill acidc. No connector contact on formationd.Battery was short-circuited during handling (terminal

damage will identify this)e. Battery is part of a whole string that received no

formation currentf. For a-d, batteries must be scrapped; for e batteries

may be put back through formation although they maynot form properly and it is safer to scrap them also.

2. Low-voltage (L2. Low-voltage (L2. Low-voltage (L2. Low-voltage (L2. Low-voltage (LV) batterV) batterV) batterV) batterV) battery (<2.000 V/cell)y (<2.000 V/cell)y (<2.000 V/cell)y (<2.000 V/cell)y (<2.000 V/cell)a. One or more cells shorted outb.Low acid fill weightc. Poor connector contact on formationd.Battery was partially short-circuited during handling

(terminal damage)e. Battery is part of a string that received very low

formation currentf. Battery is poorly formed, went onto formation heavily

sulfatedg.Early formation kickout malfunction not reinitiated (all

batteries affected)h. The usual procedure is to scrap any LV battery

3. Recharge-categor3. Recharge-categor3. Recharge-categor3. Recharge-categor3. Recharge-category batteries (voltage is >Ly batteries (voltage is >Ly batteries (voltage is >Ly batteries (voltage is >Ly batteries (voltage is >LV butV butV butV butV butbelow “acceptable”)below “acceptable”)below “acceptable”)below “acceptable”)below “acceptable”)

a. Slightly low acid fill weightb.Slightly inferior connector contact during formationc. Formed adjacent to dead battery in series-parallel

matrix formation (less-than-normal Ah input)d.One or more cells may have an incipient hard short or

hydration shorts in the separatore. Missing or damaged/leaking vent valvef. Large air leak due to cracked case or seriously

defective sealg. Incomplete formation (high PbO level in PAM), poor

acid penetration/no restsh. If all batteries in a bay are recharge category; check

rectifier/power supply setting (may be low)i. If all batteries in one string of a series-parallel array are

recharge category-low string current draw, otherstring(s) may be HV

j. Ambient temperature low for CV or TC formationalgorithm (all batteries affected)

k. Formation kicked out prematurely, not reinitiated (allbatteries affected)

l. Battery terminals corroded or oxidized

4. High-voltage (HV) batteries, >~2.2 V/cell4. High-voltage (HV) batteries, >~2.2 V/cell4. High-voltage (HV) batteries, >~2.2 V/cell4. High-voltage (HV) batteries, >~2.2 V/cell4. High-voltage (HV) batteries, >~2.2 V/cella. String draws too-high current in series- parallel array;

all batteries in string are HVb.All batteries in a bay are HV; check for high rectifier/

power supply settingc. Formation kicked out; reinitiates from the beginning

(too-high Ah input, high weight losses for all batteriesin a bay)

d.Ambient temperature high for CV or TC formationalgorithm, high Ah input (all batteries affected)

5. High impedance r5. High impedance r5. High impedance r5. High impedance r5. High impedance readingseadingseadingseadingseadingsa. Fill weights too lowb.Batteries over-formed, high weight losses

(probably HV category also)c. Incomplete formation (dead, LV or recharge

category also)d.Poor plate processing, usually at cure/drye. Meter probes too high on terminalsf. Meter probes corroded or oxidizedg. Impedance meter out of calibrationh. Battery terminals corroded or oxidized



6. High-rate discharge (HRD) voltage r6. High-rate discharge (HRD) voltage r6. High-rate discharge (HRD) voltage r6. High-rate discharge (HRD) voltage r6. High-rate discharge (HRD) voltage reading too loweading too loweading too loweading too loweading too lowa. Battery over-formed or incompletely formed, high

impedance creates large voltage drop on HRD(impedance reject)

b.Poor battery internal connections (affects HRD but notimpedance measurements- impedance is a “no-load”test)

c. HRD tester probes and/or battery terminals corrodedor oxidized

d.Poor connection of tester probes to battery terminalse. Discharge current set too high or HRD tester out of

calibrationf. Poor electrolyte distribution between separator and

plates (too little in plates)g.Low active-material porosities, restricted electrolyte

diffusionh. Plate stack compression too low, results in poor

separator/plate contacti. Grid-PAM passivation layer present

15.6. Battery Tear-Down and Analysis1. Negative plate shows ar1. Negative plate shows ar1. Negative plate shows ar1. Negative plate shows ar1. Negative plate shows areas of white lead sulfateeas of white lead sulfateeas of white lead sulfateeas of white lead sulfateeas of white lead sulfate

a. Insufficient formation Ah inputb.Fill-to-form time too long, too much lead sulfate formed

(high resistance)c. Long fill-to-form time, no carbon black in expanderd.High impurity level, lowers hydrogen over potential,

negative can’t be formede. Too much oxygen recombination due to low fill weight

and/or high formation weight loss (too much voidspace in the separator)

f. p:n value too low (<~0.8), negative- plate sulfate can’tall form out

g.Solutions: use high-purity materials, increase carbonblack amount, use p:n ratio >/=1.0

h. CV formation voltage and/or temperature too low

2. Positive plate shows ar2. Positive plate shows ar2. Positive plate shows ar2. Positive plate shows ar2. Positive plate shows areas of white lead sulfateeas of white lead sulfateeas of white lead sulfateeas of white lead sulfateeas of white lead sulfatea. Insufficient formation Ah inputb.Fill-to-form time too long, as in 1bc. High impurity level, lowers oxygen over potential,

positive material can’t be formedd.High Ah input into grid corrosion, doesn’t go into lead

sulfate conversione. High negative-plate voltage (flooded?) doesn’t allow

sufficient positive-plate polarization to complete CVformation

f. CV formation voltage and/or temperature too low

3. Excessive grid corr3. Excessive grid corr3. Excessive grid corr3. Excessive grid corr3. Excessive grid corrosion after forosion after forosion after forosion after forosion after formationmationmationmationmationa. Poor filling process created watery or dry areas,

rampant alkaline corrosion occurred in these areas(the grid or areas of it may be completely corrodedafter formation)

b.Dry areas in separator occur during filling due to tightfiber structure, trapped air (very localized), againalkaline corrosion occurs

c. Low negative-plate potential pushes positive potentialinto high-corrosion region in CV formation (occurs overentire plates)

d.Formation Ah input and/or temperature are too highe. Impurities present (chloride, organic compounds that

break down to form acetic acid) catalyze extensivegrid corrosion

4. High levels of unfor4. High levels of unfor4. High levels of unfor4. High levels of unfor4. High levels of unformed oxide, parmed oxide, parmed oxide, parmed oxide, parmed oxide, particularly in theticularly in theticularly in theticularly in theticularly in thepositive platepositive platepositive platepositive platepositive plate

a. Low Ah input, batteries under formedb.High percentage of formation charge goes into heat

production, gassing, grid corrosionc. Heavy gassing doesn’t allow acid, water penetration

into plate interiors during formation (use rest periods)d.Dense lead sulfate layer on plate surfaces (too-fine

oxide, heavy calendering during pasting, too long fill-to-form time) inhibits fluid penetration

e. High orthorhombic PbO level in the positive pastecreates an impervious structure for liquid penetration

5. High alpha:beta-PbO5. High alpha:beta-PbO5. High alpha:beta-PbO5. High alpha:beta-PbO5. High alpha:beta-PbO22222 ratio in P ratio in P ratio in P ratio in P ratio in PAMAMAMAMAMa. Increases with >temperatureb.Decreases with >acid densityc. Decreases with >current densityd.Decreases with increasing amount of positive-paste

sulfate contente. Generally, lack of acid penetration increases alpha-

PbO2 percentagef. High alpha-PbO2 levels form in areas of the plate stack

where the fill electrolyte is dilute; most prevalent inthin-plate products, pastes with little or no sulfation(high density)


References

16. References[1][1][1][1][1] G. Zguris, Batteries International, April, 1991, pp. 80-81

[2][2][2][2][2] H. Chen, et al. Journal of Power Sources 59 (1996), pp.59-62.

[3][3][3][3][3] C. Ressel, Batteries International, April, 1990, pp. 24-25

[4][4][4][4][4] Exide Technologies, First Semi-Annual Report, March2001.

[5][5][5][5][5] R.F.Nelson, The Battery Man, May 1998.

[6][6][6][6][6] R.F.Nelson, Batteries International, 36, July 1998, 95-103.

[7][7][7][7][7] K. Matthes, B. Papp and R.F. Nelson, Power Sources 12,T. Keily and B. Baxter, eds., 1988, p.1.

[8][8][8][8][8] A.Ferreira, J.Power Sources 78 (1999), 41-45

[9][9][9][9][9] The Battery Man, January 1995.

[10][10][10][10][10] J.Power Sources 67 (1997).

[11][11][11][11][11] A.Ferreira, Batteries International, 46, Jan 2001, 43-50

[12][12][12][12][12] J.Power Sources 73 (1998) 60.

[13][13][13][13][13] M.J.Weighall, ALABC Project No. R/S-001, Final Report,October 2000.

[14][14][14][14][14] CSIRO, ALABC Project S1.1, Progress Report 1, July-December 2000.

[15][15][15][15][15] R.F.Nelson, Batteries International, 43, April 2000, 51-60

[16][16][16][16][16] R.F.Nelson, Batteries International, 34, Jan 1998, 87-93

[17][17][17][17][17] G.Zguris, 16th Annual Battery Conference onApplications and Advances (2001), 163-168.

[18][18][18][18][18] Hovosorb® Technical Manual, April 1993.

[19][19][19][19][19] M.J.Weighall, ALABC Project No. R/S-001, Final Report,October 2000, 44.

[20][20][20][20][20] A.Ferreira, Batteries International, 36, July 1998, 83-90.

[21][21][21][21][21] Dr D.Berndt, Oxygen Cycle Meeting, 7ELBC, Dublin,Ireland, 19th September 2000

[22][22][22][22][22] P.R. Stevenson and O. Enoki, Proceedings of the 5th ERASeminar, London, U.K., April, 1988 Paper 3.2

[23][23][23][23][23] R.F. Nelson and M. A. Kepros, Proceedings of the 14th

Long Beach Battery Conference, IEEE, 1999, pp. 281-287

[24][24][24][24][24] R.S. Robinson and J.M. Tarascon, J. Power Sources 48(1994), 277-84

Table 2.Typical AC Impedance Values For A Variety Of Thin-PlateVRLA Single Cells And Batteries Fully Charged At 25ºC.

2V/2.5Ah Cell 5.0 milliohms

6V/2.5Ah Battery 15.0 milliohms

2V/5.0Ah Cell 3.5 milliohms

6V/5.0Ah Battery 10.0 milliohms

2V/25Ah Cell 1.5 milliohms

12V/25Ah Battery(Hawker SBS) 7.0 milliohms

12V/25Ah Battery(Hawker Genesis) 5.0 milliohms

12V/35Ah Battery(Hawker SBS) 5.5 milliohms

12V/36Ah Battery(Hawker Genesis) 4.5 milliohms

6V/100Ah Battery 1.8 milliohms

By comparison, thicker-plate VRLA productshave the following published impedance values:

12V/2Ah Yuasa Battery 80 milliohms2V/2.6Ah Portable

Energy Products Cell 30 milliohms2V/4.3Ah Portable

Energy Products Cell 24 milliohms


References

Table 3.Sample OCV Chart Used in Manufacturing to Sort Cells or Batteries After Formation or Recharge

Days Off Form HV A Categories B R LV-Dead4 >2.199 2.199 - 2.170 2.169 - 2.140 <2.140 <1.9995 >2.196 2.196 - 2.167 2.166 - 2.137 <2.137 <1.9996 >2.194 2.194 - 2.165 2.164 - 2.135 <2.135 <1.9997 >2.192 2.192 - 2.163 2.162 - 2.133 <2.133 <1.9998 >2.190 2.190 - 2.161 2.160 - 2.131 <2.131 <1.9999 >2.188 2.188 - 2.159 2.158 - 2.129 <2.129 <1.999

10 >2.186 2.186 - 2.157 2.156 - 2.127 <2.127 <1.99911 >2.185 2.185 - 2.156 2.155 - 2.126 <2.126 <1.99912 >2.184 2.184 - 2.155 2.154 - 2.125 <2.125 <1.99913 >2.183 2.183 - 2.154 2.153 - 2.124 <2.124 <1.99914 >2.182 2.182 - 2.153 2.152 - 2.123 <2.123 <1.99915 >2.181 2.181 - 2.152 2.151 - 2.123 <2.123 <1.99916 >2.180 2.180 - 2.151 2.150 - 2.123 <2.123 <1.99917 >2.179 2.179 - 2.150 2.149 - 2.123 <2.123 <1.99918 >2.178 2.178 - 2.149 2.148 - 2.123 <2.123 <1.99919 >2.177 2.177 - 2.148 2.147 - 2.123 <2.123 <1.99920 >2.176 2.176 - 2.147 2.146 - 2.123 <2.123 <1.99921 >2.175 2.175 - 2.146 2.145 - 2.123 <2.123 <1.99922 >2.174 2.174 - 2.145 2.144 - 2.123 <2.123 <1.99923 >2.173 2.173 - 2.144 2.143 - 2.123 <2.123 <1.99924 >2.172 2.172 - 2.143 2.142 - 2.123 <2.123 <1.99925 >2.172 2.172 - 2.143 2.142 - 2.123 <2.123 <1.99926 >2.171 2.171 - 2.142 2.141 - 2.123 <2.123 <1.99927 >2.170 2.170 - 2.141 2.140 - 2.123 <2.123 <1.99928 >2.169 2.169 - 2.140 2.139 - 2.123 <2.123 <1.99929 >2.168 2.168 - 2.139 2.138 - 2.123 <2.123 <1.99930 >2.168 2.168 - 2.139 2.138 - 2.123 <2.123 <1.99931 >2.167 2.167 - 2.138 2.137 - 2.123 <2.123 <1.99932 >2.166 2.166 - 2.137 2.136 - 2.123 <2.123 <1.99933 >2.165 2.165 - 2.136 2.135 - 2.123 <2.123 <1.99934 >2.164 2.164 - 2.135 2.134 - 2.123 <2.123 <1.99935 >2.164 2.164 - 2.135 2.134 - 2.123 <2.123 <1.99936 >2.163 2.163 - 2.134 2.133 - 2.123 <2.123 <1.99937 >2.163 2.163 - 2.134 2.133 - 2.123 <2.123 <1.99938 >2.162 2.162 - 2.133 2.132 - 2.123 <2.123 <1.99939 >2.162 2.162 - 2.133 2.132 - 2.123 <2.123 <1.99940 >2.161 2.161 - 2.132 2.131 - 2.123 <2.123 <1.99941 >2.160 2.160 - 2.131 2.130 - 2.123 <2.123 <1.99942 >2.160 2.160 - 2.131 2.130 - 2.123 <2.123 <1.99943 >2.159 2.159 - 2.130 2.129 - 2.123 <2.123 <1.99944 >2.159 2.159 - 2.130 2.129 - 2.123 <2.123 <1.99945 >2.158 2.158 - 2.129 2.128 - 2.123 <2.123 <1.99946 >2.157 2.157 - 2.128 2.127 - 2.123 <2.123 <1.99947 >2.157 2.157 - 2.128 2.127 - 2.123 <2.123 <1.99948 >2.156 2.156 - 2.127 2.126 - 2.123 <2.123 <1.99949 >2.156 2.156 - 2.127 2.126 - 2.123 <2.123 <1.99950 >2.155 2.155 - 2.126 2.125 - 2.123 <2.123 <1.99951 >2.155 2.155 - 2.126 2.125 - 2.123 <2.123 <1.99952 >2.154 2.154 - 2.125 2.124 - 2.123 <2.123 <1.99953 >2.154 2.154 - 2.125 2.124 - 2.123 <2.123 <1.99954 >2.154 2.154 - 2.125 2.124 - 2.123 <2.123 <1.99955 >2.153 2.153 - 2.124 2.123 - 2.123 <2.123 <1.99956 >2.153 2.153 - 2.124 2.123 - 2.123 <2.123 <1.99957 >2.153 2.153 - 2.124 2.123 - 2.123 <2.123 <1.99958 >2.153 2.153 - 2.124 2.123 - 2.123 <2.123 <1.99959 >2.152 2.152 - 2.123 2.123 - 2.123 <2.123 <1.99960 >2.152 2.152 - 2.123 2.123 - 2.123 <2.123 <1.999


VRLAVRLAVRLAVRLAVRLA Valve Regulated Lead Acid

SLISLISLISLISLI Starting, Lighting, Ignition

UPSUPSUPSUPSUPS Uninterruptible Power Supply

VVVVV Voltage

IIIII Current

RRRRR Resistance

AhAhAhAhAh Ampere Hour

OCOCOCOCOC Open Circuit

OCVOCVOCVOCVOCV Open Circuit Voltage

TOCVTOCVTOCVTOCVTOCV Top Of Charge Voltage

EOCVEOCVEOCVEOCVEOCV End Of Charge Voltage

LLLLLVVVVV Low Voltage

HVHVHVHVHV High Voltage

CCCCCCCCCC Constant Current

CVCVCVCVCV Constant Voltage

TCTCTCTCTC Taper Current

PCPCPCPCPC Pulse Current

DCDCDCDCDC Direct Current

ACACACACAC Alternating Current

HRDHRDHRDHRDHRD High Rate Discharge

PbPbPbPbPb Lead

PbOPbOPbOPbOPbO Lead Monoxide

PbO2PbO2PbO2PbO2PbO2 Lead Dioxide

Pb3O4Pb3O4Pb3O4Pb3O4Pb3O4 Red Lead

H3PO4H3PO4H3PO4H3PO4H3PO4 Phosphoric Acid

COCOCOCOCO Carbon Monoxide

CO2CO2CO2CO2CO2 Carbon Dioxide

3BS/ TRB3BS/ TRB3BS/ TRB3BS/ TRB3BS/ TRB Tribasic Lead Sulfate

4BS/ TTB4BS/ TTB4BS/ TTB4BS/ TTB4BS/ TTB Tetrabasic Lead Sulfate

NAMNAMNAMNAMNAM Negative Active Material

PPPPPAMAMAMAMAM Positive Active Material

SEMSEMSEMSEMSEM Scanning Electron Microscope

BETBETBETBETBET Technique for surface area determination

XRDXRDXRDXRDXRD X-Ray Diffraction

S.G./ s.g.S.G./ s.g.S.G./ s.g.S.G./ s.g.S.G./ s.g. Specific Gravity

H & VH & VH & VH & VH & V Hollingsworth and Vose

AGMAGMAGMAGMAGM Absorptive Glass Mat

RBSMRBSMRBSMRBSMRBSM Recombinant Battery Separator Mat

MFGMFGMFGMFGMFG Microfine Glass

L/d ratioL/d ratioL/d ratioL/d ratioL/d ratio Plate height/ Plate spacing ratio

KpaKpaKpaKpaKpa Kilo Pascals

CFMCFMCFMCFMCFM Cubic Feet per Minute

COSCOSCOSCOSCOS Cast on Strap

Appendix

APPENDIX 1 – Glossary Of Terms And Abbreviations


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A Guide To VRLA Battery Formation Techniques