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What's the difference between Lead and Lithium batteries?

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  • [see Forum Thread this is taken from for more]

    How do I compare the value of two batteries with different chemistries?

    The value of a battery is somewhat objective because it depends on how you will use it. For example, lead batteries are much heavier than lithium batteries. There's also how much maintenance it takes, for example flooded-lead-acid batteries take a lot of special care.

    The number of times a battery can be recharged is extremely important if cycling the batteries daily. However, if the batteries are only for emergency use and only cycled a few times per year, the number of cycles isn't that important.

    How many times can a battery be cycled?
    You can get this information from the battery vendor's data sheet. Let's take a look at the Trojan SPRE 12 225:

    Capture.PNG

    If you never discharge the battery below 50%, it can be recharged almost 2000 times! But at 50%, a 200Ah battery is only a 100 Ah battery.

    50% is fairly standard for a lead acid battery before the curve starts to really flatten out. Lithium batteries on the other hand can usually go 80 or 90% depth of discharge with 1000s of cycles.

    Capture.PNG



    The Math
    The value of the batteries is the cost / kWh / DoD / number of cycles @ DoD

    So how does the SPRE 12 225 compare to the BattleBorn 100 AH 12V ?
    SPRE 12 225BattleBorn 100 AH 12V
    Cost per unit$413$949
    DoD50%90%
    Useable Energy Watt hours225*12* 50% = 13501080
    Cycle Life at DoD19003000
    $/kW as emergency backup$306$879
    $/kW/cycle$0.161$0.29
    It looks like the SPRE 12 is as good or better than Lithium, right? Not so fast! After 3000 cycles the Battle Born batteries are guaranteed to be operating at least at 80%; those batteries can continue to be used. But, the lead acid batteries are essentially at end of life. Plus, the SPRE 12 are flooded lead acid batteries; skimp on the maintenance and they will have short life spans. Also, check the next post, lead acid batteries lose 10% more power while charging/discharging than LiFePO4, that's like loosing 1 in every 10 panels!

    If you'd like to see how various factors affect a LiFePO4, check out a datasheet for them such as this one.
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