How Many Cycles Can I Expect from My Battery?

DELIVERING QUALITY SINCE 1952.

Why Is It So Difficult To Answer This Simple Question:

“How Many Cycles Can I Expect From My Battery?”

10.14.15Special thanks to our strategic partner Texas Instruments for the

charts and graphs contained in the in this presentation.

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Expected Number of Cycles

There are many factors involved in predicting cycle life of a battery pack.– Chemistry selected/used– Amount of time the battery is exposed to temperature extremes.– Average charge state the battery is in.

• Charge voltage

– High discharge and charge rates (localized internal heating)

– Pack design and construction • High current path routes / cells exposed to same load• Inner cells and thermal management

– Number of series cells and parallel cells• Cell balancing

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Expected Number of Cycles

Chemistry Selected/Used– The core chemistry plays a large role in the cycle life of the battery. There

are always tradeoffs, however.• 20 to 50 cycles, Li-Sulfur• 300 to 500 cycles, Li-Ion • 1000 to 3000 cycles, LiFePO4• 20000 cycles Li-Titanate, Li4Ti5O12

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Expected Number of Cycles

Amount of time the battery is exposed to temperature extremes.

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Expected Number of Cycles

Charge Voltage Affects Battery Service Life– The higher the voltage, the higher the initial capacity– Overcharging shortens battery cycle life

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Expected Number of Cycles

Charge Current versus Battery Degradation– Charge Current:

• Limited to 1C rate to prevent overheating that can accelerate degradation

– Some new cells can handle higher-rate

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Expected Number of Cycles

Pack Design and Construction– High current path routes / cells exposed to same load– Internal Cells and thermal gradients

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Expected Number of Cycles

Series Cells, Full Pack Limited by Cell ImbalanceCell misbalance can cause significant degradation to battery pack performance and cycle life

– When the first cell becomes full, charge must stop– When first cell becomes empty, discharge must stop– Weak cells will age faster than strong cells– Weakest cell ultimately limits pack usable energy (weakest link)– Systematic temperature gradients in the pack weaken cells running at

higher average temperature– Without balancing, at every cycle the voltage difference between the

weakest and strongest cell increases– Eventually one cell will always be near the

maximum voltage and another cell nearthe minimum voltage => can notcharge or discharge pack

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Expected Number of Cycles

Capacitive current redistribution – more complex implementation, no energy loss. Low balancing rate. Moderate size requirements.

Inductive current redistribution – most complex implementation, no energy loss. High balancing rate can be supported. Highest size requirements

Current bypass (Passive) – simplest method, but some energy loss. Both high and low rates can be implemented. Easy to integrate, small size and cost.

Cell Balancing

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In Summary the primary factors that affect cycle life are:– Chemistry selected/used– Amount of time the battery is exposed to

temperature extremes.– Average charge state the battery is in.

• Charge voltage

– High discharge and charge rates (localized internal heating)

– Pack design and construction • High current path routes / cells exposed to

same load• Inner cells and thermal management

– Number of series cells and parallel cells• Cell balancing

Summary

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Our Products

Battery Packs Flex & Rigid-Flex PCB’s User Interfaces

Fans & Motors Cable Assemblies Printed Circuit Boards

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Design Centers & Technical Support

Battery Pack & Power Management – Denver, CO User Interfaces – Largo, FL Fans & Motors – Wales, UK PCB’s – New Bedford, MA & Shenzhen, China Flex & Rigid Flex – Toronto, Canada Cable Assemblies – New Bedford, MA

Our Engineering and Design teams are ready to help our customers create world class and cost effective product solutions.

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Q&A

Questions?– Enter any questions you may have

in the Control Panel

– If we don’t have time to get to it, wewill reply via email

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Thank YouCheck out our previous webinars at www.epectec.com.

For more information email sales@epectec.com.

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