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Thread: Battery Cycle - what defines a cycle

  1. #1
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    Battery Cycle - what defines a cycle

    I see battery cycle mentioned regularly...

    I now have a battery that counts the cycles.....and damned if I can see any consistency

    Given I run LiFePO4 what does a battery have to go through to click over another cycle?

  2. #2
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    Battery Cycle - what defines a cycle

    A cycle by definition is a discharge/charge event regardless of DoD.

    Some define it though as a full discharge/recharge cycle which is not fully correct.

    If you have a battery hanging on solar, charging up
    Daily and being used - it’s life for 2000 cycles is around 5.4 years.
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    Quote Originally Posted by Tombie View Post
    A cycle by definition is a discharge/charge event regardless of DoD.

    Some define it though as a full discharge/recharge cycle which is not fully correct.

    If you have a battery hanging on solar, charging up
    Daily and being used - it’s life for 2000 cycles is around 5.4 years.
    That’s how I understood it......but it doesn’t register a cycle each time it gets back to 100% which is weird.

  4. #4
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    The depth of discharge of a battery discharge/charge cycle significantly affects the life of the battery.

    Here's an example from the specs of a typical 12 volt LiFePO4 battery


    • Cycles @ 100% DOD: DOD 2000 Cycles
    • Cycles @ 80% DOD: DOD 3000 Cycles
    • Cycles @ 50% DOD: DOD 3500 Cycles
    • Cycles @ 30% DOD: DOD 8000 Cycles



    As you can see the batterys life is much greater with shallow discharge cycles. I don't see how the batterys electronics 'counting' discharge cycles is particularly relevant to anything at all and may just be a marketing/sales gimmick.

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    That is an enormous difference in the number of cycles.

    It helps to explain why the Hybrid Camry battery management tries to ensure that the hybrid battery operates between 40% and 60% almost all of the time and it tries even harder to ensure that it never gets above 80%.

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    Quote Originally Posted by vnx205 View Post
    That is an enormous difference in the number of cycles.

    It helps to explain why the Hybrid Camry battery management tries to ensure that the hybrid battery operates between 40% and 60% almost all of the time and it tries even harder to ensure that it never gets above 80%.
    Not really. If you take a battery as a finite amount of energy and recharges...

    Take it down 100% 2000 times.
    Take it down 50% is not quite double (3500 times).
    Using less than a 3rd at a go goes you smaller bites more often.

    Although not technically spot on - you get 2000ISH allotments of energy. How you take that out determines how many “fractions” of energy you get from the ‘pool’.
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  7. #7
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    Actually, the figures are pretty normal, except for the number of cycles down to 50%.

    I am guessing that is an error and it is somewhere between 4,500 and 4,800.

    The amount of cycles available from any given battery, be it lithium or lead acid, is based on that particular battery's total Throughput over the normal life span of that battery.

    While the number of cycles will vary slightly over the range of 100% up to 30%, the total throughput is usually similar across the whole range.

    In the case of the battery DeanoH has used as an example, the total Throughput is around 240,000 amperes over the battery's normal life span.

    Hence 2,000 cycles down to 100% discharge ( DoD ) equals a total Throughput of 200,000 amperes over the battery's normal life span

    3,000 cycles down to 80% DoD = 240,000 amperes

    4,800 cycles down to 50% DoD ( should read ) = 240,000 amperes

    8,000 cycles down to 30$ D0D = 240,000 amperes

  8. #8
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    I hadn't thought of that issue of a small number of big bites of the available energy as opposed to a lot more smaller bites adding up to the same total.

    So is the limited operating range of a hybrid vehicle battery more to do with temperature? There seems to be a lot of information about suggesting that overheating is detrimental.

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  9. #9
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    Quote Originally Posted by vnx205 View Post
    So is the limited operating range of a hybrid vehicle battery more to do with temperature? There seems to be a lot of information about suggesting that overheating is detrimental.
    Hi mate and sorry I can't help you there, I have had very little experience with Hybrid vehicle lithium battery setups.

  10. #10
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    really roughly

    lets call a nominated "cycle" being a charge from say 30%-90% of the capacity and then discharged from 90%-30% of the capacity. We'll also stipulate that this is done at a given rate.

    Lets say you have 2000 of these up your sleeve.

    if you did nice things to the battery like discharging it slower and charging it slowly to 98% that might only count as .7 of a cycle

    if you only pulled 10% out that might be .05 of a cycle

    but if you used all of the capacity of the battery and pulled it all out hard with no letting up then you dumped all of it back in with no cooldown and no remorese that might count as 5 cycles.


    At the end of the day, It sort of follows Peukert's law but instead of amps draw it counts charges and discharges.

    Some battery manufacturers give you the specs for what counts as a cycle others just let you guess.
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