Sharing Battery Knowledge

People want easy-to-read battery information. To share knowledge, I condensed the

material from Batteries in a Portable World, a book I wrote, into essays and

created www.BatteryUniversity.com. The website went on the air in 2003 and

quickly became a popular resource of battery information worldwide. New material

is being added as it becomes available.

Much of my writing comes from my personal experience working with batteries. I

also draw on test results from our own laboratories at Cadex. While laboratory

analyses have their rightful place, I respect the opinions of battery users,

especially the feedback from BatteryUniversity.com. This interface with the user

gives me an advantage in learning how the battery behaves in the field. Such

information is, in my opinion, more important than regurgitating reams of

laboratory tests. The critical mass speaks louder than fancy brochures and

printed specifications.

There is no black and white in the battery field, only many shades of gray. The

battery behaves much like us folks its a black box with a mind and mood of its

own; its mystical and unexplainable. For some users, the battery causes no

problems at all; for others its nothing but a problem.

When looking at a battery we must keep in mind that it is electrochemical. Its a

vessel that is slow to fill, holds relatively little storage capacity and has a

defined life span. Although critical improvements have been made over the years,

the progress is marginal compared with the vast advancements in microelectronics.

As long as the battery relies on an electrochemical process, limitations will

prevail.

As there is no perfect spouses or ideal employees, so also have batteries

strengths and limitations. The manufacturer has the choices of building a battery

for long runtimes and low cost, but this pack will have a limited service life.

Another variety is high load capabilities but this pack will be bulky. A third

group offers extended life but the battery is heavy and expensive.

Manufacturers of electronic devices base the performance on a perfect battery, a

condition that only exists when the battery is new. Runtime, low cost and safety

have been the number one criteria, and in consumer products longevity is often

neglected. With the electric vehicle, this emphasis is changing, a move that will

benefit the battery industry immensely. Meanwhile, there are ways to prolong

batteries and BatteryUniversity.com will assist.

BatteryUniversity.com is written for the professional user who needs a basic

understanding of battery behavior. It also served the ordinary user who wants to

get the more life out of a pack. The website stresses the strengths and

limitations of the battery, explains different battery types and provides useful

hints in choosing a battery. The website is easy and entertaining to read and

makes minimal use of technical jargon. BatteryUniversity.com addresses only

commercially available batteries and only mentions new developments in passing.

Since my background is electrical, I tackle batteries from the electrical side

and less on chemical reaction.

When was the Battery Invented?

One of the most remarkable and novel discoveries in the last 400 years was

electricity. We might ask, Has electricity been around that long? The answer is

yes, and perhaps much longer, but its practical use has only been at our disposal

since the mid to late 1800s, and in a limited way at first. One of the earliest

public works gaining attention was enlightening the 1893 Chicagos World Columbia

Exposition with 250,000 light bulbs, and illuminating a bridge over the river

Seine during the 1900 World Fair in Paris.

The use of electricity may go back further. While constructing a railway in 1936

near Baghdad, workers uncovered what appeared to be a prehistoric battery, also

known as the Parthian Battery. The object dates back to the Parthian period and

is believed to be 2,000 years old. The battery consisted of a clay jar that was

filled with a vinegar solution into which an iron rod surrounded by a copper

cylinder was inserted. This device produced 1.1 to 2.0 volts of electricity.

Figure 1 illustrates the Parthian Battery.

.

Figure 1: Parthian Battery. A clay jar of a prehistoric battery holds an iron rod

surrounded by a copper cylinder. When filled with vinegar or electrolytic

solution, the jar produces 1.1 to 2 volts.

Not all scientists accept the Parthian Battery as a source of energy. It is

possible that the device was used for electroplating, such as adding a layer of

gold or other precious metals to a surface. The Egyptians are said to have

electroplated antimony onto copper over 4,300 years ago. Archeological evidence

suggests the Babylonians were the first to discover and employ a galvanic

technique in the manufacturing of jewelry by using an electrolyte based on grape

juice to gold plate stoneware. The Parthians, who ruled Baghdad (ca. 250 BC), may

have used batteries to electroplate silver.

One of the earliest methods to generate electricity in modern times was through

creating a static charge. In 1660, Otto von Guericke constructed an electrical

machine using a large sulfur globe which, when rubbed and turned, attracted

feathers and small pieces of paper. Guericke was able to prove that the sparks

generated were electrical in nature.

The first practical use of static electricity was the electric pistol, which

Alessandro Volta (17451827) invented. He thought of providing long-distance

communications, albeit only one Boolean bit. An iron wire supported by wooden

poles was to be strung from Como to Milan, Italy. At the receiving end, the wire

would terminate in a jar filled with methane gas. To signal a coded event, an

electrical spark would be sent by wire for the purpose of detonating the electric

pistol. This communications link was never built. Figure 1-2 shows a pencil

rendering of Alessandro Volta.

Figure 2: Alessandro Volta, inventor

of the electric battery

Voltas discovery of the

decomposition of water by an

electrical current laid the

foundation of electrochemistry.

Courtesy of Cadex

In 1791, while working at Bologna University, Luigi Galvani discovered that the

muscle of a frog would contract when touched by a metallic object. This

phenomenon became known as animal electricity. Prompted by these experiments,

Volta initiated a series of experiments using zinc, lead, tin and iron as

positive plates (cathode); and copper, silver, gold and graphite as negative

plates (anode). The interest in galvanic electricity soon became widespread.

Early Batteries

Volta discovered in 1800 that certain fluids would generate a continuous flow of

electrical power when used as a conductor. This discovery led to the invention of

the first voltaic cell, more commonly known as the battery. Volta discovered

further that the voltage would increase when voltaic cells were stacked on top of

each other. Figure 3 illustrates such a serial connection.

Figure 1-3: Four variations

of Voltas electric battery

Metals in a battery have

different electrical effects.

Volta noticed that the voltage

potential with dissimilar

substances got stronger the

farther apart they were from

one another.

The first number in the metals

listed below is the affinity to

attract electrons; the second

is the standard potential from

the first oxidation state.

Zinc = 1.6 / -0.76 V

Lead = 1.9 / -0.13 V

Tin = 1.8 / -1.07 V

Iron = 1.8 / -0.04 V

Copper = 1.9 / 0.159 V

Silver = 1.9 / 1.98 V

Gold = 2.4 / 1.83 V

Carbon = 2.5 / 0.13 V

The metals determine the

battery voltage; they were

separated with moist paper

soaked in salt water.

Courtesy of Cadex

In the same year, Volta released his discovery of a continuous source of

electricity to the Royal Society of London. No longer were experiments limited to

a brief display of sparks that lasted a fraction of a second. An endless stream

of electric current now seemed possible.

France was one of the first nations to officially recognize Voltas discoveries.

This was during a time when France was approaching the height of scientific

advancements and new ideas were welcomed with open arms, helping to support of

the countrys political agenda. By invitation, Volta addressed the Institute of

France in a series of lectures at which Napoleon Bonaparte was present as a

member of the institute (see Figure 4).

Figure 4: Voltas

experimentations at the

Institute of France

Voltas discoveries so

impressed the world that

in November 1800 the

French National Institute

invited him to lectures

at events in which

Napoleon Bonaparte

participated. Napoleon

helped with the

experiments, drawing

sparks from the battery,

melting a steel wire,

discharging an electric

pistol and decomposing

water into its elements.

Courtesy of Cadex

In 1800, Sir Humphry

Davy, inventor of the miners safety lamp, began testing the chemical effects of

electricity and found out that decomposition occurred when passing electrical

current through substances. This process was later called electrolysis. He made

new discoveries by installing the worlds largest and most powerful electric

battery in the vaults of the Royal Institution of London. Connecting the battery

to charcoal electrodes produced the first electric light. Witnesses reported that

his voltaic arc lamp produced the most brilliant ascending arch of light ever

seen.

In 1802, William Cruickshank designed the first electric battery for mass

production. Cruickshank arranged square sheets of copper with equal-sized sheets

sizes of zinc. These sheets were placed into a long rectangular wooden box and

soldered together. Grooves in the box held the metal plates in position, and the

sealed box was then filled with an electrolyte of brine, or a watered-down acid.

This resembled the flooded battery that is still with us today. Figure 5

illustrates the battery workshop of Cruickshank.

Figure 5: Cruickshank and the

first flooded battery. William

Cruickshank, an English chemist,

built a battery of electric cells

by joining zinc and copper plates

in a wooden box filled with an

electrolyte solution. This flooded

design had the advantage of not

drying out with use and provided

more energy than Voltas disc

arrangement.

Courtesy of Cadex

Invention of the Rechargeable

Battery

In 1836, John F. Daniell, an

English chemist, developed an

improved battery that produced a

steadier current than earlier

devices. Until this time, all

batteries were primary, meaning

they could not be recharged. In

1859, the French physicist Gaston

Plant invented the first

rechargeable battery. It was based

on lead acid, a system that is

still used today.

In 1899, Waldmar Jungner from Sweden invented the nickel-cadmium battery (NiCd),

which used nickel for the positive electrode (cathode) and cadmium for the

negative (anode). High material costs compared to lead acid limited its use and

two years later, Thomas Edison produced an alternative design by replacing

cadmium with iron. Low specific energy, poor performance at low temperature and

high self-discharge limited the success of the nickel-iron battery. It was not

until 1932 that Shlecht and Ackermann achieved higher load currents and improved

the longevity of NiCd by inventing the sintered pole plate. In 1947, Georg

Neumann succeeded in sealing the cell.

For many years, NiCd was the only rechargeable battery for portable applications.

In the 1990s, environmentalists in Europe became concerned about environmental

contamination if NiCd were carelessly disposed; they began to restrict this

chemistry and asked the consumer industry to switch to Nickel-metal-hydride

(NiMH), an environmentally friendlier battery. NiMH is similar to NiCd, and many

predict that NiMH will be the stepping-stone to the more enduring lithium-ion

(Li-ion).Most research activities today revolve around improving lithium-based

systems. Besides powering cellular phones, laptops, digital cameras, power tools

and medical devices, Li-ion is also used for electric vehicles. The battery has a

number of benefits, most notably its high specific energy, simple charging, low

maintenance and being environmentally benign.

Electricity Through Magnetism

The discovery of how to generate electricity through magnetism came relatively

late. In 1820, Andr-Marie Ampre (17751836) noticed that wires carrying an

electric current were at times attracted to and at other times repelled from one

another. In 1831, Michael Faraday (17911867) demonstrated how a copper disc

provided a constant flow of electricity while revolving in a strong magnetic

field. Faraday, assisting Davy and his research team, succeeded in generating an

endless electrical force as long as the movement between a coil and magnet

continued. This led to the invention of the electric generator, and reversing the

process enabled the electric motor. Shortly thereafter, transformers were

developed that converted alternating current (AC) to any desired voltage. In

1833, Faraday established the foundation of electrochemistry on which Faradays

law is based. Faradays law of induction relates to electromagnetism linked to

transformers, inductors, and many types of electrical motors and generators.

Once the relationship with magnetism was understood, large generators began

producing a steady flow of electricity. Motors followed that enabled mechanical

movement, and the Edison light bulb appeared to conquer darkness. After George

Westinghouse lit up Chicago's World Columbian Exposition in 1893, Westinghouse

built three large generators to transform energy from the Niagara Falls to

electricity. The three-phase AC technology developed by Nikola Tesla enabled

transmission lines to carry electric power over great distances. Electricity was

thus made widely available to humanity to improve the quality of life.

Figure 6: 250,000 light bulbs illuminate Chicago's World Columbian Exposition in

1893.

The success of the electric light led to building three large hydro generators at

Niagara Falls.

Courtesy of the Brooklyn Museum Archives. Goodyear Archival Collection

The invention of the electronic vacuum tube in the early 1900s formed the

significant next step towards high technology, enabling frequency oscillators,

signal amplifications and digital switching. This led to radio broadcasting in

the 1920s and the first digital computer, called ENIAC, in 1946. The discovery of

the transistor in 1947 paved the way for the arrival of the integrated circuit 10

years later, and the microprocessor ushered in the Information Age, forever

changing the way we live and work.

Humanity depends on electricity, and with increased mobility people have

gravitated more and more towards portable power first for wheeled applications,

then portability and finally wearable use. As awkward and unreliable as the early

batteries may have been, future generations may look at todays technologies as

nothing more than clumsy experiments.

Battery Developments

Inventions in the 1700s and 1800s are well documented and credit goes to the

dignified inventors. Benjamin Franklin invented the Franklin stove, bifocal

eyeglasses and the lightning rod. He was unequaled in American history as an

inventor until Thomas Edison emerged. Edison was a good businessman who may have

taken credit for inventions others had made. Contrary to popular belief, Edison

did not invent the light bulb; he improved upon a 50-year-old idea by using a

small, carbonized filament lit up in a better vacuum. Although a number of people

had worked on this idea before, Edison gained the financial reward by making the

concept commercially viable to the public. The phonograph is another success

story for which Edison received due credit.

Countries often credit their own citizens for having made important inventions,

whether or not they deserve it. When visiting museums in Europe, the USA and

Japan one sees such bestowment. The work to develop the car, x-ray machines,

telephones, broadcast radio, televisions and computers might have been done in

parallel, not knowing of others advancements at that time, and the rightful

inventor is often not clearly identified. Similar uncertainties exist with the

invention of new battery systems, and we give respect to research teams and

organizations rather than individuals. Table 1 summarizes battery advancements

and lists inventors when available.

Year Inventor Activity

1600 William Gilbert (UK) Establishment of electrochemistry study

1791 Luigi Galvani (Italy) Discovery of animal electricity

1800

1802

1820

Alessandro Volta (Italy)

William Cruickshank (UK)

Andr-Marie Ampre (France)

Invention of the voltaic cell (zinc, copper

disks)

First electric battery capable of mass

1833

1836

1839

1859

1868

1899

Michael Faraday (UK)

John F. Daniell (UK)

William Robert Grove (UK)

Gaston Plant (France)

Georges Leclanch (France)

Waldmar Jungner (Sweden)

production

Electricity through magnetism

Announcement of Faradays law

Invention of the Daniell cell

Invention of the fuel cell (H2/O2)

Invention of the lead acid battery

Invention of the Leclanch cell (carbon-

zinc)

Invention of the nickel-cadmium battery

1901

1932

1947

1949

1970s

1990

1991

1994

1996

1996

Thomas A. Edison (USA)

Shlecht & Ackermann (D)

Georg Neumann (Germany)

Lew Urry, Eveready Battery

Group effort

Group effort

Sony (Japan)

Bellcore (USA)

Moli Energy (Canada)

University of Texas (USA)

Invention of the nickel-iron battery

Invention of the sintered pole plate

Successfully sealing the nickel-cadmium

battery

Invention of the alkaline-manganese battery

Development of valve-regulated lead acid

battery

Commercialization of nickel-metal-hydride

battery

Commercialization of lithium-ion battery

Commercialization of lithium-ion polymer

Introduction of Li-ion with manganese

cathode

Identification of Li-phosphate (LiFePO4)

2002 University of Montreal,

Quebec Hydro, MIT, others

Improvement of Li-phosphate, nanotechnology,

commercialization

Table 1: History of modern battery development. No new major battery system has

entered the commercial market since the invention of Li-phosphate in 1996.

Battery Developments

Inventions in the 1700s and 1800s are well documented and credit goes to the

dignified inventors. Benjamin Franklin invented the Franklin stove, bifocal

eyeglasses and the lightning rod. He was unequaled in American history as an

inventor until Thomas Edison emerged. Edison was a good businessman who may have

taken credit for inventions others had made. Contrary to popular belief, Edison

did not invent the light bulb; he improved upon a 50-year-old idea by using a

small, carbonized filament lit up in a better vacuum. Although a number of people

had worked on this idea before, Edison gained the financial reward by making the

concept commercially viable to the public. The phonograph is another success

story for which Edison received due credit.

Countries often credit their own citizens for having made important inventions,

whether or not they deserve it. When visiting museums in Europe, the USA and

Japan one sees such bestowment. The work to develop the car, x-ray machines,

telephones, broadcast radio, televisions and computers might have been done in

parallel, not knowing of others advancements at that time, and the rightful

inventor is often not clearly identified. Similar uncertainties exist with the

invention of new battery systems, and we give respect to research teams and

organizations rather than individuals. Table 1 summarizes battery advancements

and lists inventors when available.

Year Inventor Activity

1600 William Gilbert (UK) Establishment of electrochemistry study

1791 Luigi Galvani (Italy) Discovery of animal electricity

1800

1802

1820

1833

1836

1839

1859

1868

1899

Alessandro Volta (Italy)

William Cruickshank (UK)

Andr-Marie Ampre

(France)

Michael Faraday (UK)

John F. Daniell (UK)

William Robert Grove (UK)

Gaston Plant (France)

Georges Leclanch (France)

Waldmar Jungner (Sweden)

Invention of the voltaic cell (zinc, copper

disks)

First electric battery capable of mass

production

Electricity through magnetism

Announcement of Faradays law

Invention of the Daniell cell

Invention of the fuel cell (H2/O2)

Invention of the lead acid battery

Invention of the Leclanch cell (carbon-

zinc)

Invention of the nickel-cadmium battery

1901

1932

1947

1949

Thomas A. Edison (USA)

Shlecht & Ackermann (D)

Georg Neumann (Germany)

Lew Urry, Eveready Battery

Invention of the nickel-iron battery

Invention of the sintered pole plate

Successfully sealing the nickel-cadmium

battery

Invention of the alkaline-manganese battery

1970s

1990

1991

1994

1996

1996

Group effort

Group effort

Sony (Japan)

Bellcore (USA)

Moli Energy (Canada)

University of Texas (USA)

Development of valve-regulated lead acid

battery

Commercialization of nickel-metal-hydride

battery

Commercialization of lithium-ion battery

Commercialization of lithium-ion polymer

Introduction of Li-ion with manganese

cathode

Identification of Li-phosphate (LiFePO4)

2002 University of Montreal,

Quebec Hydro, MIT, others

Improvement of Li-phosphate,

nanotechnology, commercialization

Table 1: History of modern battery development. No new major battery system has

entered the commercial market since the invention of Li-phosphate in 1996.

Global Battery Markets

The battery market is expanding, and the global revenue in 2009 was a whopping

$47.5 billion.* With the growing demand for portable electronics and the desire

to connect and work outside the confines of four walls, experts predict that this

figure will reach $74 billion in 2015. These numbers are speculative and include

batteries for the electric powertrain of cars.

An Overview of Battery Types

Batteries are divided into two categories: primary and secondary. In 2009,

primary batteries made up 23.6 percent of the global market. Frost & Sullivan

(2009) predict a 7.4 percent decline of the primary battery in revenue

distribution by 2015. Primary batteries are used in watches, electronic keys,

remote controls, childrens toys, light beacons and military devices.

The real growth lies in secondary batteries. Frost & Sullivansay that

rechargeable batteriesaccount for 76.4 percent of the global market, a number

that is expected to increase to 82.6 percent in 2015. Batteries are also

classified by chemistry and the most common are lithium-, lead-, and nickel-based

systems. Figure 1 illustrates the distribution of these chemistries.

Figure 1: Revenue contributions by different battery chemistries

Courtesy of Frost & Sullivan (2009)

Lithium-ion is the battery of choice for consumer products, and no other systems

threaten to interfere with its dominance at this time. The lead acid market is

similar in size to Li-ion. Here the applications are divided into SLI (starter

battery) for automotive, stationary for power backup, and deep-cycle for wheeled

mobility such as golf cars, wheelchairs and scissor lifts. Lead acid holds a

solid position, as it has done for the last hundred years. There are no other

systems that threaten to unseat this forgiving and low-cost chemistry any time

soon.

High specific energy and long storage has made alkaline more popular than carbon-

zinc, which Georges Leclanch invented in 1868. The environmentally benign

nickel-metal-hydride (NiMH) continues to hold an important role, as it replaces

many applications previously served by nickel-cadmium (NiCd). However, at only

three percent market share, NiMH is a minor player in the battery world and will

likely relinquish more of its market to Li-ion by 2015.

Developing nations will contribute to future battery sales, and new markets are

the electric bicycle in Asia and storage batteries to supply electric power to

remote communities in Africa and other parts of the world. Wind turbines, solar

power and other renewable sources also use storage batteries for load leveling.

The large grid storage batteries used for load leveling collect surplus energy

from renewable resources during high activity and supply extra power on heavy

user demand. Read more about Batteries for Stationary, Grid Storage.

A major new battery user might be the electric powertrain for personal cars.

However, battery cost and longevity will dictate how quickly the automotive

sector will adopt this new propulsion system. Energy from oil is cheap,

convenient and readily available; any alternative faces difficult challenges.

Government incentives may be provided, but such intervention distorts the true

cost of energy, shields the underlying problem with fossil fuel and only

satisfies certain lobby groups through short-term solutions.

During the last five years or so, no new battery system has emerged that can

claim to offer disruptive technology. Although much research is being done, no

new concept is ready to enter the market at the time of writing, nor are new

developments close to breakthrough point. There are many reasons for this

apparent lack of progress: few products have requirements that are as stringent

as the battery. For example, battery users want low price, long life, high

specific energy, safe operation and minimal maintenance. In addition, the battery

must work at hot and cold temperatures, deliver high power on demand and charge

quickly. Only some of these attributes are achievable with various battery

technologies.

Most consumers are satisfied with the battery performance on portable devices.

Todays battery technology also serves power backup and wheeled mobility

reasonably well. Using our current battery technology for electric powertrains on

cars, however, might prove difficult because the long-term effects in that

environment are not fully understood. The switch to a power source offering a

fraction of the kinetic energy compared to fossil fuels will be an eye-opener for

motorists who continually demand larger vehicles with more. Read more about the

Cost of Power.

Advancements in Batteries

Batteries advance on two fronts, and these developments reflect themselves in

increased specific energy for longer runtimes and improved specific power for

good power delivery on demand. Figure 2 illustrates the energy and power

densities of lead acid, nickel-cadmium (NiCd), nickel-metal-hydride (NiMH) and

the Li-ion family (Li-ion).

Figure 1-8: Specific energy and specific power of rechargeable batteries.

Specific energy is the capacity a battery can hold in watt-hours per kilogram

(Wh/kg); specific power is the batterys ability to deliver power in watts per

kilogram (W/kg).

Rechargeable lithium-metal batteries (Li-metal) were introduced in the 1980s, but

instability with metallic lithium on the anode prompted a recall in 1991. Its

high specific energy and good power density are challenging manufacturers revisit

into this powerful chemistry again. Enhanced safety may be possible by mixing

metallic lithium with tin and silicon. Experimental Li-metal batteries achieve

300Wh/kg, a specific energy that is of special interest to the electric vehicle.

Read more about Experimental Rechargeable Batteries.

* All references to dollar ($) pricing are in US dollars at the time of writing.

Getting to Know the Battery

The battery dictates the speed with which mobility advances. So important is this

portable energy source that any incremental improvement opens new doors for many

products. The better the battery, the greater our liberty will become.

Besides packing more energy into the battery, engineers have also made strides in

reducing power consumption of portable equipment. These advancements go hand-in-

hand with longer runtimes but are often counteracted by the demand for additional

features and more power. The end result is similar runtimes but enhanced

performance.

The battery has not advanced at the same speed as microelectronics, and the

industry has only gained 8 to 10 percent in capacity per year during the last two

decades. This is a far cry from Moores Law* that specifies a doubling of the

number of transistors in an integrated circuit every two years. Instead of two

years, the capacity of lithium-ion took 10 years to double.

In parallel with achieving capacity gain, battery makers must also focus on

improving manufacturing methods to ensure better safety. The recent recall of

millions of lithium-cobalt packs caused by thermal runaway is a reminder of the

inherent risk in condensing too much energy into a small package. Better

manufacturing practices should make such recalls a thing of the past. A

generation of Li-ion batteries is emerging that are built for longevity. These

batteries have a lower specific energy (capacity) than those for portable

electronics and are increasingly being considered for the electric powertrain of

vehicles.

People want an inexhaustible pool of energy in a package that is small, cheap,

safe and clean, and the battery industry can only fulfill this desire partially.

As long as the battery is an electrochemical process, there will be limitations

on capacity and life span. Only a revolutionary new storage system could satisfy

the unquenchable thirst for mobile power, and its anyones guess whether this

will be lithium-air, the fuel cell, or some other ground-breaking new power

generator, such as atomic fusion. For most of us, the big break might not come in

our lifetime.

Meeting Expectations

Many battery novices argue, wrongly, that all advanced battery systems offer high

energy densities, deliver thousands of charge/discharge cycles and come in a

small size. While some of these attributes are possible, this is not attainable

in one and the same battery in a given chemistry.

A battery may be designed for high specific energy and small size, but the cycle

life is short. Another battery may be built for high load capabilities and

durability, and the cells are bulky and heavy. A third pack may have high

capacity and long service life, but the manufacturing cost is out of reach for

the average consumer. Battery manufacturers are well aware of customer needs and

respond by offering products that best suit the application intended. The mobile

phone industry is an example of this clever adaptation. The emphasis is on small

size, high energy density and low price. Longevity is less important here.

The terms nickel-metal-hydride (NiMH) and lithium-ion (Li-ion) do not

automatically mean high specific energy. For example, NiMH for the electric

powertrain in vehicles has a specific energy of only 45Wh/kg, a value that is not

much higher than lead acid. The consumer NiMH, in comparison, has about 90Wh/kg.

The Li-ion battery for hybrid and electric vehicles can have a specific energy as

low as 60Wh/kg, a value that is comparable with nickel-cadmium. Li-ion for cell

phones and laptops, on the other hand, has two to three times this specific

energy.

The Cadex-sponsored website www.BatteryUniversity.com generates many interesting

questions. Those that stand out are, Whats the best battery for a remote-

controlled car, a portable solar station, an electric bicycle or electric car?

There is no universal battery that fits all needs and each application is unique.

Although lithium-ion would in most instances be the preferred choice, high price

and the need for an approved protection circuit exclude this system from use by

many hobbyists and small manufacturers. Removing Li-ion leads back to the nickel-

and lead-based options. Consumer products may have benefited the most from

battery advancements. High volume made Li-ion relatively inexpensive.

Will the battery replace the internal combustion engine of cars? It may come as a

surprise to many that we dont yet have an economical battery that allows long-

distance driving and lasts as long as the car. Batteries work reasonably well for

portable applications such as cell phones, laptops and digital cameras. Low power

enables an economical price; the relative short battery life is acceptable in

consumer products; and we can live with a decreasing runtime. While the fading

capacity can be annoying, it does not endanger safety.

As we examine the characteristics of battery systems and compare alternative

power sources, such as the fuel cell and the internal combustion (IC) engine, we

realize that the battery is best suited for portable and stationary systems. For

motive applications such as trains, ocean going ships and aircraft, the battery

lacks capacity, endurance and reliability. The dividing line, in my opinion, lies

with the electric vehicle.

* In 1965, Gordon Moore said that the number of transistors in an integrated

circuit would double every two years. The prediction became true and is being

carried into the 21st century. Applied to a battery, Moores Law would shrink a

starter battery in a car to the size of a coin.

Comparing the Battery with other Power Sources

This article begins with the positive traits of the battery, and then moves into

the limitations when compared with other power sources.

Energy storage

Batteries store energy well and for a considerable length of time. Primary

batteries (non-rechargeable) hold more energy than secondary (rechargeable), and

the self-discharge is lower. Alkaline cells are good for 10 years with minimal

losses. Lead-, nickel- and lithium-based batteries need periodic recharges to

compensate for lost power.

Specific energy (Capacity)

A battery may hold adequate energy for portable use, but this does not transfer

equally well for large mobile and stationary systems. For example, a 100kg

(220lb) battery produces about 10kWh of energy an IC engine of the same weight

generates 100kW.

Responsiveness

Batteries have a huge advantage over other power sources in being ready to

deliver on short notice think of the quick action of the camera flash! There is

no warm-up, as is the case with the internal combustion (IC) engine; the power

from the battery flows within a fraction of a second. In comparison, a jet engine

takes several seconds to gain power, a fuel cell requires a few minutes, and the

cold steam engine of a locomotive needs hours to build up steam.

Power bandwidth

Rechargeable batteries have a wide power bandwidth, a quality that is shared with

the diesel engine. In comparison, the bandwidth of the fuel cell is narrow and

works best within a specific load. Jet engines also have a limited power

bandwidth. They have poor low-end torque and operate most efficiently at a

defined revolution-per-minute (RPM).

Environment

The battery runs clean and stays reasonably cool. Sealed cells have no exhaust,

are quiet and do not vibrate. This is in sharp contrast with the IC engine and

larger fuel cells that require noisy compressors and cooling fans. The IC engine

also needs air and exhausts toxic gases.

Efficiency

The battery is highly efficient. Below 70 percent charge, the charge efficiency

is close to 100 percent and the discharge losses are only a few percent. In

comparison, the energy efficiency of the fuel cell is 20 to 60 percent, and the

thermal engines is 25 to 30 percent. (At optimal air intake speed and

temperature, the GE90-115 on the Boeing 777 jetliner is 37 percent efficient.)

Installation

The sealed battery operates in any position and offers good shock and vibration

tolerance. This benefit does not transfer to the flooded batteries that must be

installed in the upright position. Most IC engines must also be positioned in the

upright position and mounted on shock- absorbing dampers to reduce vibration.

Thermal engines also need air and an exhaust.

Operating cost

Lithium- and nickel-based batteries are best suited for portable devices; lead

acid batteries are economical for wheeled mobility and stationary applications.

Cost and weight make batteries impractical for electric powertrains in larger

vehicles. The price of a 1,000-watt battery (1kW) is roughly $1,000 and it has a

life span of about 2,500 hours. Adding the replacement cost of $0.40/h and an

average of $0.10/kWh for charging, the cost per kWh comes to about $0.50. The IC

engine costs less to build per watt and lasts for about 4,000 hours. This brings

the cost per 1kWh to about $0.34. Read more about the Battery Against Fossil

Fuel.

Maintenance

With the exception of watering of flooded lead batteries and discharging NiCds to

prevent memory, rechargeable batteries require low maintenance. Service

includes cleaning of corrosion buildup on the outside terminals and applying

periodic performance checks.

Service life

The rechargeable battery has a relatively short service life and ages even if not

in use. In consumer products, the 3- to 5-year lifespan is satisfactory. This is

not acceptable for larger batteries in industry, and makers of the hybrid and

electric vehicles guarantee their batteries for 8 to 10 years. The fuel cell

delivers 2,000 to 5,000 hours of service and, depending on temperature, large

stationary batteries are good for 5 to 20 years.

Temperature extremes

Like molasses, cold temperatures slow the electrochemical reaction and batteries

do not perform well below freezing. The fuel cell shares the same problem, but

the internal combustion engine does well once warmed up. Charging must always be

done above freezing. Operating at a high temperature provides a performance boost

but this causes rapid aging due to added stress. Read about Discharging at High

and Low Temperatures.

Charge time

Here, the battery has an undisputed disadvantage. Lithium- and nickel-based

systems take 1 to 3 hours to charge; lead acid typically takes 14 hours. In

comparison, filling up a vehicle only takes a few minutes. Although some electric

vehicles can be charged to 80 percent in less than one hour on a high-power

outlet, users of electric vehicles will need to make adjustments.

Disposal

Nickel-cadmium and lead acid batteries contain hazardous material and cannot be

disposed of in landfills. Nickel-metal-hydrate and lithium systems are

environmentally friendly and can be disposed of with regular household items in

small quantities. Authorities recommend that all batteries be recycled.

Battery Definitions

Batteries come in all shapes and sizes and there could be as many types as there

are species of dog. Rather than giving batteries unique names as we do with pets,

we distinguish batteries by chemistry, voltage, size, specific energy (capacity),

specific power, (delivery of power) and more. A battery can operate as a single

cell to power a cellular phone, or be connected in series to deliver several

hundred volts to serve a UPS (uninterruptible power supply system) and the

electric powertrain of a vehicle. Some batteries have high capacity but cannot

deliver much power, while a starter battery has a relatively low capacity but can

crank the engine with 300A.

The largest battery systems are used for grid storage to store and delivery

energy derived from renewable power sources such as wind turbines and solar

systems. A 30-megawatt (MW) wind farm uses a storage battery of about 15MW. This

is the equivalent of 20,000 starter batteries and costs about $10 million. One

mega-watt feeds 50 houses or a super Walmart store. Lets now examine each of the

battery characteristics further.

Chemistry

The most common chemistries are lead, nickel and lithium. Each system requires

its own charging algorithm. Unless provisions are made to change the charge

setting, different battery chemistries cannot be interchanged in the same

charger. Also observe the chemistry when shipping and disposing of batteries;

each type has a different regulatory requirement.

Voltage

The imprinted voltage refers to the nominal battery voltage. Always observe the

correct voltage when connecting to a load or a charger. Do not proceed if the

voltage differs. The open circuit voltage (OCV) on a fully charged battery can be

slightly higher than the nominal; the closed circuit voltage (CCV) represents the

battery voltage under load or on charge and the readings will vary accordingly.

Capacity

Capacity represents the specific energy in ampere-hours (Ah). Manufacturers often

overrate a battery by giving a higher Ah rating than it can provide. You can use

a battery with different Ah (but correct voltage), provided the rating is high

enough. Chargers have some tolerance to batteries with different Ah ratings. A

larger battery will take longer to charge than a small one.

Cold cranking amps (CCA)

CCA specifies the ability to draw high load current at 18C (0F) on starter

batteries. Different norms specify dissimilar load durations and end voltages.

See Abbreviations / Conversions.

Specific energy and energy density

Specific energy or gravimetric energy density defines the battery capacity in

weight (Wh/kg); energy density or volumetric energy density is given in size

(Wh/l). A battery can have a high specific energy but poor specific power (load

capability), as is the case in an alkaline battery. Alternatively, a battery may

have a low specific energy but can deliver high specific power, as is possible

with the supercapacitor. Specific energy is synonymous with battery capacity and

runtime.

Specific power

Specific power or gravimetric power density indicates the loading capability, or

the amount of current the battery can provide. Batteries for power tools exhibit

high specific power but have reduced specific energy (capacity). Specific power

is synonymous with low internal resistance and the delivery of power.

C-rates

C-rates specify charge and discharge currents. At 1C, the battery charges and

discharges at a current that is par with the marked Ah rating; at 0.5C the

current is half, and at 0.1C it is one tenth. On charge, 1C charges a good

battery in about one hour; 0.5C takes 2 hours and 0.1C 10 to 14 hours. Read more

about What is the C-rate?

Load

A load draws energy from the battery. Internal battery resistance and depleting

state-of-charge cause the voltage to drop. Physical work over time is energy

measured in Watt-hours (Wh).

Watts and Volt-amps (VA)

Power drawn from a battery is expressed in watts (W) or volt-amps (VA). Watt is

the real power that is being metered; VA is the apparent power that determines

the wiring sizing and the circuit breakers. On a purely resistive load, watt and

VA readings are alike; a reactive load such as an inductive motor or florescent

light causes a drop in the power factor (pf) from the ideal one (1) to 0.7 or

lower. For example, a pf of 0.7 has a power efficiency of 70.

Primary Batteries

The growth has been in secondary batteries (rechargeable) but non-rechargeable or

primary batteries are equally important. They continue to fill an important niche

market in applications such as wristwatches, remote controls, electric keys and

childrens toys. Primary batteries also assist when charging is impractical or

impossible, such as military combat, rescue missions and forest-fire services.

Other applications of primary batteries are tire pressure gauges in cars and

trucks, transmitters for bird tracking, pacemakers for heart patients,

intelligent drill bits for mining,as well as light beacons and remote repeater

stations. High specific energy, long storage times and operational readiness make

this battery well suited for such applications. The battery can be carried to

remote locations and used instantly, even after long storage. Most primary

batteries are inexpensive, readily available and environmentally friendly.

Carbon-zinc, also known as the Leclanch battery, is the least expensive battery

and comes with consumer devices when batteries are included. These general

purpose batteries are used for applications with low power drain, such as remote

controls, flashlights, childrens toys and wall clocks. One of the most common

primary batteries for consumers is the alkaline-manganese, or alkaline for short.

Lewis Urry invented it in 1949 while working with the Eveready Battery Company

Laboratory in Parma, Ohio. Alkaline delivers more energy at higher load currents

than carbon-zinc. Best of all, alkaline does not leak when depleted, as carbon-

zinc does. On the negative side, alkaline is more expensive than carbon-zinc.

Primary batteries have one of the highest energy densities. Although secondary

batteries have improved, a regular household alkaline provides 50 percent more

energy than lithium-ion. The most energy-dense primary is the lithium battery

made for film cameras and military combat. It holds more than three times the

energy of lithium-ion and comes in various blends, such as lithium-metal, lithium

manganese dioxide, lithium-sulfur dioxide, lithium-thionyl chloride, lithium

oxygen and others. Figure 1 compares the typical gravimetric energy densities of

lead acid, NiMH, Li-ion, alkaline and lithium primary batteries.

Figure 1: Specific energy comparison of secondary and primary batteries

Secondary batteries are typically rated at 1C; alkaline uses much lower discharge

currents.

Courtesy of Cadex

Specific energy indicates the energy a battery can hold. This, however, does not

guarantee delivery. Primary batteries tend to have high internal resistance,

which limits the discharge to light loads such as remote controls, flashlights

and portable entertainment devices. Digital cameras are borderline a power

drill on alkaline would be unthinkable.

Manufacturers of primary batteries only specify specific energy; the specific

power (ability to deliver power) is not published. While most secondary batteries

are rated at a discharge current of 1C, the capacity of primary batteries is

measured by discharging them at a very low current of 25mA, or a fraction of a C.

In addition, the batteries are allowed to go down to a very low voltage of 0.8

volts per cell. This evaluation method provides impressive readings on paper, but

the results are poor under a more demanding load.

Figure 2 compares performance of primary and secondary batteries on a discharge

of 1C. The results are indicated in Actual and Rated. Actual is the Wh/kg derived

at a 1C discharge, Rated is the Wh/kg the manufacturer specifies when discharged

at a much low current. While the primary batteries do well on a discharge

representing entertainment device, secondary batteries have lower capacities but

are more resilient at a load of 1C.

Figure 2: Energy comparison under load. Rated refers to a mild discharge;

Actual is a load at 1C. High internal resistance limits alkaline battery to

light loads.

Courtesy of Cadex

The reason for the sharp performance drop on primary batteries is the high

internal resistance, which causes the voltage to drop under load. The already

high resistance increases further as the battery depletes on discharge. When the

battery goes flat on a digital camera, for example, precious capacity is often

left behind. A spent alkaline can often power a kitchen clock for two years.

Figure 2 above shows the largest discrepancy between Rated and Actual on

alkaline. A long-life alkaline (not shown on chart) will deliver better results.

Table 3 illustrates the capacity of standard alkaline batteries with loads that

are typical of personal entertainment devices or small flashlights. Discharging

at fractional C-rates produces high capacities; increasing the discharge rate

would drastically reduce it.

Table 3: Alkaline specifications. The discharge resembles entertainment devices

with low loads.

Courtesy of Panasonic

The use of primary batteries can be expensive, and the inability to recharge

increases the cost of power by about thirty fold over secondary batteries. The

pricing issue becomes even more acute if the packs are being replaced after each

mission, regardless of length of service. Discarding partially used batteries is

common, especially in fleet applications and critical missions. It is more

convenient and safer to simply issue the troops fresh packs with each call rather

than estimating the remaining state-of-charge. A US Army general once said that

half of the batteries discarded still have 50 percent energy left.

Estimating the battery state-of-charge would help, but such instruments are

expensive and inaccurate. The most basic method is measuring the open circuit

voltage and reading the internal resistance by applying a brief load and checking

the voltage drop. A large voltage differential would relate to rising resistance,

a hint to the end of life. A more accurate way is to count the out-flowing

energy, a measurement that is also known as coulomb counting, but this requires

expensive circuitry. See How to Measure State-of-charge. Due to high cost and

inherent inaccuracies, fuel gauges are seldom used on primary batteries.

Choices of Primary Batteries

Early batteries were used mainly for experimental purposes. Voltages fluctuated

under load and made them impractical for most applications. In 1836, John F.

Daniell, an English chemist, developed an improved battery that offered more

stable current delivery and was suitable to supply power to telegraph networks

since electrical distribution networks did not exist at the time. These early

batteries were non-rechargeable (primary) and it was not until 1859 when the

French physician Gaston Plant invented the first rechargeable battery based on

the lead acid chemistry. Read more about When Was the Battery Invented?

Carbon-zinc, also known as the Leclanch battery, was one of the first commercial

batteries. The early Leclanch cell in 1876 was wet, and the dry cell was

developed in 1886. The first consumer carbon-zinc batteries for flashlights

appeared in 1898, a development that formed the Eveready battery company. Carbon-

zinc is the least expensive battery and normally comes with consumer devices when

batteries are included. These general purpose batteries are used for low power

drain applications, such as remote controls, flashlights, childrens toys and

wall clocks.

One of the most common primary batteries for consumers is the alkaline-manganese,

or Alkaline for short. Lewis Urry invented the Alkaline in 1949 while working

with the Eveready Battery Company Laboratory in Parma, Ohio. Alkaline delivers

more energy at higher load currents than carbon-zinc and it does not leak when

depleted, although it is not totally leak-proof. A discharging Alkaline generates

hydroxide gases. Pressure buildup can rupture the seal and cause corrosion in

form of a feathery crystalline structure that can spread to neighboring parts and

cause damage. All primary batteries produce gas on discharge. Portable devices

with these batteries must have provision for venting.

Lithium Iron Disulfide (Li-FeS2) is a newcomer to the primary battery family and

offers improved performance. Lithium batteries normally deliver 3 volts and

higher, but Li-FeS2 produces 1.5 volts to serve as an alternative of alkaline and

carbon-zinc in the AA and AAA formats. It has a higher capacity and a lower

internal resistance than Alkaline. This enables moderate to heavy loads and is

ideal for digital cameras. Further advantages are improved low temperature

performance, superior leakage resistance and low self-discharge, allowing 15

years of storage at ambient temperatures. Low weight and minimal toxicity are

added benefits.

The disadvantages of the Li-FeS2 are a higher price and transportation issues

because of the lithium metal content in the anode. This causes restriction in air

shipment. In 2004, the US DOT and the Federal Aviation Administration (FAA)

banned bulk shipments of primary lithium batteries on passenger flights, but

airline passengers can still carry them on board or in checked bags. Each AA-

sized Li-FeS2 contains 0.98 grams of lithium; the air limitation of primary

lithium batteries is 2 grams (8 grams for rechargeable Li-ion). This restricts

each passenger to two cells; however, exceptions are made and 12 batteries can be

carried as samples. Read more about How to Transport Batteries.

The Li-FeS2 includes safety devices in the form of a resettable PTC thermal

switch that limits the current at high temperature. The Li-FeS2 cell cannot be

recharged as is possible with NiMH in the AA and AAA formats. Recharging, putting

in a cell backwards or mixing with used batteries or other battery types could

cause a leak or explosion. Read more about Health Concerns with Batteries.

Figures 1 and 2 compare the discharge voltage and internal resistance of

Alkaline and Li-FeS2 at a 50mA pulsed load. Of interest is the flat voltage curve

and the low internal resistance of Lithium; Alkaline shows a gradual voltage drop

and a permanent increase in resistance with use. This shortens the runtime,

especially at an elevated load.

Figure 1: Voltage and internal

resistance of Alkaline on

discharge.

The voltage drops rapidly and

causes the internal resistance

to rise

Figure 2: Voltage and internal

resistance of Lithium on

discharge.

The voltage curve is flat and

the internal resistance stays

low

Both images are courtesy of

Energizer

The AA and AAA are the most common cell formats. Known as penlight batteries for

pocket lights, the AA became available to the public in 1915 and was used as a

spy tool during World War I; the American National Standard Institute

standardized the format in 1947. The AAA was developed in 1954 to reduce the size

of the Kodak and Polaroid cameras and shrink other portable devices. In the

1990s, an offshoot of the 9V battery produced the AAAA for laser pointers, LED

penlights, computer styli, and headphone amplifiers. Read more about A look at

Old and New Battery Packaging. Table 3 compares carbon-zinc, alkaline, lithium,

NiCd, NiMH and nickel-zinc and the AA and AAA cell sizes.

Carbon-zinc Alkaline Lithium

(Li-FeS2) NiCd NiMH

Capacity* AA

AAA

400-1,700

~300

1,800-2,800

800-1,200

2,500-3,400

1,200

600-1,000

300-500

800-2,700

600-1,250

Nominal V 1.50 1.50 1.50 1.20 1.20

Discharge

Rate Very low Low Medium Very high Very high

Rechargeable No No No Yes Yes

Shelf life 1-2 years 7 years 10-15 years 3-5 years 3-5 years

Leak

resistance Poor Good Superior Good Good

Retail ** AA

AAA

Not

available

in most

$0.40-2.80

$1.50-2.80

$3.00-5.00

$4.00-5.00

Not

available

in most

$4.00-5.00

$4.00-5.00

stores stores

Table 3: Summary of batteries available in AA and AAA format. The capacity on the

AA is double that of the AAA at similar price, making the energy storage cost of

the AAA twice than that of the AA.

* In mAh; discharge current is less than 500mA

** Estimated prices in $US (2012)

The AAA cell contains roughly half the capacity of the larger AA at a similar

price. In essence, the energy cost of the AAA is twice that of the AA. In an

effort to downsize, energy cost often takes second stage and device manufacturers

prefer using the smaller AAA over the larger AA. This is the case with many

bicycle lights where the AA format would only increase the device slightly but

deliver twice the energy for the same battery cost. Proper design considerations

help protect the environment by generating less waste.

Retail prices of the Alkaline AA vary, so does performance. Exponent, a US

engineering firm, checked the capacity of eight brand-name alkaline batteries in

AA packages and discovered a discrepancy between the best and lowest performers

of 800 percent. A practical gauge to test batteries is counting the shots a

digital camera can take with a set of cells. The relatively high current pulses

of a digital camera stress the battery more than a remote control or a kitchen

clock would. When a regular Alkaline stops functioning in a digital camera, the

remaining energy can still power a remote control and run a kitchen clock for up

to two years.

Figure 4 illustrates the number of shots a digital camera can take with discharge

pulses of 1.3 watts on Alkaline, NiMH and Lithium Li-FeS2 in an AA package. (Two

cells put in series to get 3V, 1.3W draws 433mA.) Although the three battery

chemistries tested have similar capacities, the results in form of pulse counts

vary largely. The clear winner is Li-FeS2 with 690 pulses; the second is NiMH

with 520 pulses and the distant third is standard Alkaline producing only 85

pulses. Internal resistance rather than capacity governs the shot count here.

Read more about How to Rate Battery Runtime.

Figure 4: Number of shots a

digital camera can take

with Alkaline NiMH and

Lithium

Li-FeS2, NiMH and Alkaline

have similar capacities;

the internal resistance

governs the shot count on a

digital camera. Li-FeS2,

3Ah, 690 pulses

NiMH, 2.5Ah, 520 pulses

Alkaline, 3Ah, 85 pulses

Test: ANSI C18.1

Courtesy of Exponent

The rated capacity as a performance indicator is most useful at low discharge

currents; at higher loads the power factor begins to play an important role. The

relationship between capacity and the ability to deliver current can best be

illustrated with a Ragone Chart. Read more about Calculating Battery Runtime.

Named after David V. Ragone, the Ragone chart evaluates an energy storage device

on energy and power.

References

Presentation by Dan Durbin, Energizer Applications support, Medical Device &

Manufacturing (MD&M) West, Anaheim, CA, 15 February 2012

Presentation by Quinn Horn, Ph.D., P.E. Exponent, Inc. Medical Device &

Manufacturing (MD&M) West, Anaheim, CA, 15 February 2012

Comparison Table of Secondary Batteries

Rechargeable batteries play an important role in our life and many daily chores

would be unthinkable without the ability to recharge an empty battery. Points of

interest are specific energy, years of service life, load characteristics,

safety, price, self-discharge, environmental issues, maintenance requirements,

and disposal.

Lead Acid One of the oldest rechargeable battery systems; is rugged, forgiving

if abused and economical in price; has a low specific energy and limited cycle

life. Lead acid is used for wheelchairs, golf cars, personnel carriers, emergency

lighting and uninterruptible power supply (UPS).

Nickel-cadmium (NiCd) Mature and well understood; is used where long service

life, high discharge current, extreme temperatures and economical price are of

importance. Due to environmental concerns, NiCd is being replaced with other

chemistries. Main applications are power tools, two-way radios, aircraft and UPS.

Nickel-metal-hydride (NiMH) A practical replacement for NiCd; has higher

specific energy with fewer toxic metals. NiMH is used for medical instruments,

hybrid cars and industrial applications. NiMH is available in AA and AAA cells

for consumer use.

Lithium-ion (Li-ion) Most promising battery systems; is used for portable

consumer products as well as electric powertrains for vehicles; is more expensive

than nickel- and lead acid systems and needs protection circuit for safety. The

lithium-ion family is divided into three major battery types, so named by their

cathode oxides, which are cobalt, manganese and phosphate. The characteristics of

these Li-ion systems are as follows.

Lithium-ion-cobalt or lithium-cobalt (LiCoO2): Has high specific energy with

moderate load capabilities and modest service life. Applications include cell

phones, laptops, digital cameras and wearable products.

Lithium-ion-manganese or lithium-manganese (LiMn2O4): Is capable of high charge

and discharge currents but has low specific energy and modest service life; used

for power tools, medical instruments and electric powertrains.

Lithium-ion-phosphate or lithium-phosphate (LiFePO4): Is similar to lithium-

manganese; nominal voltage is 3.3V/cell; offers long cycle life, has a good safe

record but exhibits higher self-discharge than other Li-ion systems.

There are many other lithium-ion based batteries, some of which are described

further on this website. Missing in the list is also the popular lithium-ion-

polymer, or Li-polymer. While Li-ion systems get their name from their unique

cathode materials, Li-polymer differs by having a distinct architecture. Nor is

the rechargeable lithium-metal mentioned. This battery requires further

development to control dendrite growth, which can compromise safety. Once solved,

Li-metal will become an alternative battery choice with extraordinary high

specific energy and good specific power.

Table 1 compares the characteristics of four commonly used rechargeable battery

systems showing average performance ratings at time of publication.

Table 1: Characteristics of commonly used rechargeable batteries

The figures are based on average ratings of commercial batteries at time of

publication; experimental batteries with above-average ratings are excluded.

1 Internal resistance of a battery pack varies with milliampere-hour (mAh) rating,

wiring and number of cells. Protection circuit of lithium-ion adds about 100m. 2 Based on 18650 cell size. Cell size and design determines internal resistance.

3 Cycle life is based on battery receiving regular maintenance.

4 Cycle life is based on the depth of discharge (DoD). Shallow DoD improves cycle

life. 5 Self-discharge is highest immediately after charge. NiCd loses 10% in the first

24 hours, then declines to 10% every 30 days. High temperature increases self-

discharge. 6 Internal protection circuits typically consume 3% of the stored energy per

month. 7

The traditional voltage is 1.25V; 1.2V is more commonly used. 8 Low internal resistance reduces the voltage drop under load and Li-ion is often

rated higher than 3.6V/cell. Cells marked 3.7V and 3.8V are fully compatible with

3.6V. 9 Capable of high current pulses; needs time to recuperate.

10 Do not charge regular Li-ion below freezing. See Charging at High and Low

Temperatures.

11 Maintenance may be in the form of equalizing or topping charge to prevent

sulfation. 12

Cut-off if less than 2.20V or more than 4.30V for most Li-ion; different

voltage settings apply for lithium-iron-phosphate.

Lead-based Batteries

Invented by the French physician Gaston Plant in 1859, lead acid was the first

rechargeable battery for commercial use. Despite its advanced age, the lead

chemistry continues to be in wide use today, and there are good reasons for its

popularity; lead acid is dependable and inexpensive on cost-per-watt base. There

are few other batteries that deliver bulk power as cheaply as lead acid, and this

makes the battery cost-effective for automobiles, golf cars, forklifts, marine

and uninterruptible power supplies (UPS).

But lead acid has disadvantages; it is heavy and is less durable than nickel- and

lithium-based systems when deep-cycled. A full discharge causes strain and each

discharge/charge cycle permanently robs the battery of a small amount of

capacity. This loss is small while the battery is in good operating condition,

but the fading increases once the performance drops to half the nominal capacity.

This wear-down characteristic applies to all batteries in various degrees.

Depending on the depth of discharge, lead acid for deep-cycle applications

provides 200 to 300 discharge/charge cycles. The primary reasons for its

relatively short cycle life are grid corrosion on the positive electrode,

depletion of the active material and expansion of the positive plates. These

changes are most prevalent at elevated operating temperatures and high-current

discharges. See How to Prolong Lead Acid Batteries.

Charging a lead acid battery is simple but the correct voltage limits must be

observed, and here there are compromises. Choosing alow voltage limit shelters

the battery but this produces poor performance and causes a buildup of sulfation

on the negative plate. A high voltage limit improves performance but form grid

corrosion on the positive plate. While sulfation can be reversed if serviced in

time, corrosion is permanent. See Charging Lead Acid.

Lead acid does not lend itself to fast charging and with most types, a full

charge takes 14 to16 hours. The battery must always be stored at full state-of-

charge. Low charge causes sulfation, a condition that robs the battery of

performance. Adding carbon on the negative electrode reduces this problem but

this lowers the specific energy. See New Lead Acid Systems.

Lead acid has a moderate life span and is not subject to memory as nickel-based

systems are. Charge retention is best among rechargeable batteries. While NiCd

loses approximately 40 percent of its stored energy in three months, lead acid

self-discharges the same amount in one year. Lead acid work well at cold

temperatures and is superior to lithium-ion when operating in subzero

conditions.

Sealed Lead Acid

The first sealed, or maintenance-free, lead acid emerge in the mid-1970s. The

engineers argued that the term sealed lead acid is a misnomer because no lead

acid battery can be totally sealed. This is true and battery designers added a

valve to control venting of gases during stressful charge and rapid discharge.

Rather than submerging the plates in a liquid, the electrolyte is impregnated

into a moistened separator, a design that resembles nickel- and lithium-bases

system. This enables to operate the battery in any physical orientation without

leakage.

The sealed battery contains less electrolyte than the flooded type, hence the

term acid-starved. Perhaps the most significant advantage of the sealed lead

acid is the ability to combine oxygen and hydrogen to create water and prevent

water loss. The recombination occurs at a moderate pressure of 0.14 bar (2psi).

The valve serves as safety vent if gases buildup during over-overcharge or

stressful discharge. Repeated venting would lead to an eventual dry out.

Driven by these advantages, several types of sealed lead acid have emerged and

the most common are gel, also known as valve-regulated lead acid (VRLA), and

absorbent glass mat (AGM). The gel cell contains a silica type gel that suspends

the electrolyte in a paste. Smaller packs with capacities of up to 30A are called

SLA (sealed lead acid). Packaged in a plastic container, these batteries are used

for small UPS, emergency lighting, ventilators for healthcare and wheelchairs.

Because of economical price, dependable service and low maintenance, the SLA

remains the preferred choice for biomedical and healthcare in hospitals and

retirement homes. The VRLA is the larger gel variant used as power backup for

cellular repeater towers, Internet hubs, banks, hospitals, airports and other

sites.

The AGM is a newer design and suspends the electrolyte in especially designed

glass mat. This offers several advantages to lead acid systems, including faster

charging and instant high load currents on demand. AGM works best as a mid-range

battery with capacities of 30 to 100Ah and is less suited for large systems, such

as UPS. Typical uses are starter batter for motorcycles, start-stop function for

micro-hybrid cars, as well as marine and RV that need some cycling.

With cycling and age, the capacity of AGM fades gradually; gel, on the other

hand, has a dome shaped performance curve and stays in the high performance range

longer but then drops suddenly towards the end of life. AGM is more expensive

than flooded, but is cheaper than gel.(Gel would be too expensive for start/stop

use in cars.) See Absorbent Glass Mat (AGM).

Unlike the flooded, the sealed lead acid battery is designed with a low over-

voltage potential to prohibit the battery from reaching its gas-generating

potential during charge. Excess charging causes gassing, venting and subsequent

water depletion and dry out. Consequently, gel, and in part also AGM, cannot be

charged to their full potential and the charge voltage limit must be set lower

than that of a flooded. The float charge on full charge must also be lowered. In

respect to charging, the gel and AGM are no direct replacements to the flooded

type. If no designated charger is available with lower voltage settings,

disconnect the charger after 24 hours of charge. This prevents gassing due to a

float voltage that is set too high. See Charging Lead Acid.

The optimum operating temperature for a VRLA battery is 25C (77F); every 8C

(15F) rise above this temperature threshold cuts battery life in half. See Heat,

Loading and Battery Life. Lead acid batteries are rated at a 5-hour (0.2C) and

20-hour (0.05C) discharge. The battery performs best when discharged slowly and

the capacity readings are notably higher at a slow discharge rate. Lead acid can,

however, deliver high pulse currents of several C if done for only a few seconds.

This makes the lead acid well suited as a starter battery, also known as starter-

light-ignition (SLI). The high lead content and the sulfuric acid make lead acid

environmentally unfriendly.

The following paragraphs look at the different architectures within the lead acid

family and explain why one battery type does not fit all.

Starter and Deep-cycle Batteries

The starter battery is designed to crank an engine with a momentary high power

burst; the deep-cycle battery, on the other hand, is built to provide continuous

power for a wheelchair or golf car. From the outside, both batteries look alike;

however, there are fundamental differences in design. While the starter battery

is made for high peak power and does not like deep cycling, the deep-cycle

battery has a moderate power output but permits cycling. Lets examine the

architectural difference between these batteries further.

Starter batteries have a CCA rating imprinted in amperes; CCA refers to cold

cranking amps, which represents the amount of current a battery can deliver at

cold temperature. SAE J537 specifies 30 seconds of discharge at 18C (0F) at

the rated CCA ampere without dropping below 7.2 volts. (SAE stands for Society of

Automotive Engineers.)

Starter batteries have a very low internal resistance, and the manufacturer

achieves this by adding extra plates for maximum surface area (Figure 1). The

plates are thin and the lead is applied in a sponge-like form that has the

appearance of fine foam. This method extends the surface area of the plates to

achieve low resistance and maximum power. Plate thickness is less important here

because the discharge is short and the battery is recharged while driving; the

emphasis is on power rather than capacity.

Figure 1: Starter battery

The starter battery has many thin plates in

parallel to achieve low resistance with high

surface area. The starter battery does not allow

deep cycling.

Courtesy of Cadex

Deep-cycle lead acid batteries for golf cars, scooters and wheelchairs are built

for maximum capacity and high cycle count. The manufacturer achieves this by

making the lead plates thick (Figure 2). Although the battery is designed for

cycling, full discharges still induce stress, and the cycle count depends on the

depth-of-discharge (DoD). Deep-cycle batteries are marked in Ah or minute of

runtime.

Figure 2: Deep-cycle battery

The deep-cycle battery has thick plates for

improved cycling abilities. The deep-cycle battery

generally allows about 300 cycles.

Courtesy of Cadex

A starter battery cannot be swapped with a deep-cycle battery and vice versa.

While an inventive senior may be tempted to install a starter battery instead of

the more expensive deep-cycle on his wheelchair to save money, the starter

battery wont last because the thin sponge-like plates would quickly dissolve

with repeated deep cycling. There are combination starter/deep-cycle batteries

available for trucks, buses, public safety and military vehicles, but these units

are big and heavy. As a simple guideline, the heavier the battery is, the more

lead it contains, and the longer it will last. Table 3 compares the typical life

of starter and deep-cycle batteries when deep-cycled.

Depth of Discharge Starter Battery Deep-cycle Battery

100%

50%

30%

1215 cycles

100120 cycles

130150 cycles

150200 cycles

400500 cycles

1,000 and more cycles

Table 3: Cycle performance of starter and deep-cycle batteries. A discharge of

100% refers to a full discharge; 50% is half and 30% is a moderate discharge with

70% remaining.

Lead is toxic and environmentalists would like to replace the lead acid battery

with another chemistry. Europe succeeded to keep nickel-cadmium batteries out of

consumer products, and authorities try to do it with the starter battery. The

choices are NiMH and lithium-ion, but at a price tag of $3,000 for Li-ion, this

will not fly. In addition, Li-ion has poor performance at sub-freezing

temperature. Regulators hope that advancements in the electric powertrain will

lower the cost, but such a large price reduction to match the low-cost lead acid

may not be possible. Lead acid will continue to be the battery of choice to crank

the engines.

Table 4 spells out the advantages and limitations of common lead acid batteries

in use today.

Advantages

Inexpensive and simple to manufacture; low cost per watt-hour

Low self-discharge; lowest among rechargeable batteries

High specific power, capable of high discharge currents

Good low and high temperature performance

Limitations

Low specific energy; poor weight-to-energy ratio

Slow charge; fully saturated charge takes 14 hours

Must be stored in charged condition to prevent sulfation

Limited cycle life; repeated deep-cycling reduces battery life

Flooded version requires watering

Transportation restrictions on the flooded type

Not environmentally friendly

Table 4: Advantages and limitations of lead acid batteries. Dry systems have

advantages over flooded but are less rugged.

Absorbent Glass Mat (AGM)

AGM technology became popular in the early 1980s as a sealed lead acid battery

for military aircraft, vehicles and UPS to reduce weight and improve reliability.

The acid is absorbed by a very fine fiberglass mat, making the battery spill-

proof. This enables shipment without hazardous material restrictions. The plates

can be made flat to resemble a standard flooded lead acid pack in a rectangular

case; they can also be wound into a cylindrical cell.

AGM has very low internal resistance, is capable to deliver high currents on

demand and offers a relatively long service life, even when deep-cycled. AGM is

maintenance free, provides good electrical reliability and is lighter than the

flooded lead acid type. It stands up well to low temperatures and has a low self-

discharge. The leading advantages are a charge that is up to five times faster

than the flooded version, and the ability to deep cycle. AGM offers a depth-of-

discharge of 80 percent; the flooded, on the other hand, is specified at 50

percent DoD to attain the same cycle life. The negatives are slightly lower

specific energy and higher manufacturing costs that the flooded. AGM has a sweet

spot in midsize packs from 30 to 100Ah and is less suitable for large UPS system.

AGM batteries are commonly built to size and are found in high-end vehicles to

run power-hungry accessories such as heated seats, steering wheels, mirrors and

windshields. NASCAR and other auto racing leagues choose AGM products because

they are vibration resistant. AGM is the preferred battery for upscale

motorcycles. Being sealed, AGM reduces acid spilling in an accident, lowers the

weight for the same performance and allows installation at odd angles. Because of

good performance at cold temperatures, AGM batteries are also used for marine,

motor home and robotic applications.

Ever since Cadillac introduced the electric starter motor in 1912, lead acid

became the natural choice to crank the engine. The classic flooded type is,

however, not robust enough for the start-stop function and most batteries in a

micro-hybrid car are AGM. Repeated cycling of a regular flooded type causes a

sharp capacity fade after two years of use. See Heat, Loading and Battery Life.

As with all gelled and sealed units, AGM batteries are sensitive to overcharging.

These batteries can be charged to 2.40V/cell (and higher) without problem;

however, the float charge should be reduced to between 2.25 and 2.30V/cell

(summer temperatures may require lower voltages). Automotive charging systems for

flooded lead acid often have a fixed float voltage setting of 14.40V

(2.40V/cell), and a direct replacement with a sealed unit could spell trouble by

exposing the battery to undue overcharge on a long drive. See Charging Lead Acid.

AGM and other sealed batteries do not like heat and should be installed away from

the engine compartment. Manufacturers recommend halting charge if the battery

core reaches 49C (120F). While regular lead acid batteries need a topping

charge every six months to prevent the buildup of sulfation, AGM batteries are

less prone to this and can sit in storage for longer before a charge becomes

necessary. Table 1 spells out the advantages and limitations of AGM.

Advantages

Spill-proof through acid encapsulation in matting technology

High specific power, low internal resistance, responsive to load

Up to 5 times faster charge than with flooded technology

Better cycle life than with flooded systems

Water retention (oxygen and hydrogen combine to produce water)

Vibration resistance due to sandwich construction

Stands up well to cold temperature

Limitations

Higher manufacturing cost than flooded (but cheaper than gel)

Sensitive to overcharging (gel has tighter tolerances than AGM)

Capacity has gradual decline (gel has a performance dome)

Low specific energy

Must be stored in charged condition (less critical than flooded)

Not environmentally friendly (has less electrolyte, lead that

flooded)

Table 4: Advantages and limitations AGM. The gel system shares many of the

characteristics.

New Lead Acid Systems

Lead acid batteries continue to hold a leading position, especially in wheeled

mobility and stationary applications. This strong market appeal entices

manufacturers to explore ways to make the batteries better. Improvements have

been made and some claims are so promising that one questions the

trustworthiness. It is no secret that researchers prefer publishing the positive

attributes while keeping the negatives under wraps. The following information on

lead acid developments was obtained from available printed resources at the time

of writing.

Firefly Energy

The composite plate material of the Firefly Energy battery is based on a lead

acid variant that is lighter, longer living and has higher active material

utilization than current lead acid systems. The battery includes foam electrodes

for the negative plates, which gives it a performance that is comparable to NiMH

but at lower manufacturing costs. Design concerns include microtubule blockage

through crystal growth during low charge conditions. In addition, crystal

expansion causes a reduction of the surface area, which will result in lower

capacity with aging. Pricing is also a concern. It currently costs about $450 to

manufacture a Firefly battery as opposed to $150 for a regular lead acid version.

Firefly Energy is a spin-off of Caterpillar and went into bankruptcy in 2010.

Altraverda Bipolar

Similar to the Firefly Energy battery, the Altraverda battery is based on lead.

It uses a proprietary titanium sub-oxide ceramic structure, called Ebonex, for

the grid and an AGM separator. The un-pasted plate contains Ebonex particles in a

polymer matrix that holds a thin lead alloy foil on the external surfaces. With

5060Wh/kg, the specific energy is about one-third larger than regular lead acid

and is comparable with NiCd. Based in the UK, Altraverda works with East Penn in

the USA, and the battery is well suited for higher voltage applications.

Axion Power

The Axion Power e3 Supercell is a hybrid battery/ultracapacitor in which the

positive electrode consists of standard lead dioxide and the negative electrode

is activated carbon, while maintaining an assembly process that is similar to

lead acid. The Axion Power battery offers faster recharge times and longer cycle

life on repeated deep discharges than what is possible with regular lead acid

systems. This opens the door for the start-stop application in micro-hybrid cars.

The lead-carbon combination of the Axion Power battery lowers the lead content on

the negative plate, which results in a weight reduction of 30 percent compared to

a regular lead acid. This, however, also lowers the specific energy to 1525Wh/kg

instead of 3050Wh/kg, which a regular lead acid battery normally provides.

CSIRO Ultrabattery

The CSIRO Ultrabattery combines an asymmetric ultracapacitor and a lead acid

battery in each cell. The capacitor enhances the power and lifetime of the

battery by acting as a buffer during charging and discharging, prolonging the

lifetime by a factor of