Just to clarify.. In lithium chemistry batteries there are several aging mechanisms. Many of them occur most often below 20% or above 80% (or 85%). There are also aging mechanisms which work more slowly the less energy is in the battery. This applies just as much to LiFePO4 as other chemistries. Obviously, each battery variation (chemistry, anode/cathode structure) is optimized in different ways but all of them are remarkably similar. For example, some specific variants seem to do just fine up to 85% instead of 80%.
As a result of the degration increase outside the 20/80 range, the recommendation for long term storage is often to charge to 80% and then make sure the battery is not permitted to self discharge below 20%. Where one can reliably maintain the batteries through periodic charges, it isn't unreasonable to charge to 30% every couple of months and keep the battery between 20 and 30%. This last option is, of course, only useful when you don't need the batteries stored with charge. For standby applications it's also best if your charger is set to allow the battery to cycle a bit instead of keeping the battery "full". That is, charge to 80% then let it sit until it drops to 75% and then recharge all at once. I do need to soften this slightly... cycling a battery up to 100% and then discharging isn't nearly as bad as dropping below 20%. This is all a game of capacity vs life vs cost. If keeping a battery at 100% only reduces its life by 10% vs using a 80% max charge, then it might be more cost effective to use a 100% since you can buy a smaller battery which may be 10% less. I'm not sure I'd set my charger to go over 95% or so even then as there are some pretty aggressive degradation methods right at 100% and sometimes it's hard to be sure if you're getting too close to that line. On the other hand, where the battery life is a small portion of the cost of a bigger product and the battery is not replaceable, limiting charge to 80 (or 85%) can push the life out further. Many android phones have a setting to limit charge to 85% to make the battery last longer as a result. On Fri, Apr 26, 2024, 2:12 PM TJ Trout <t...@voltbb.com> wrote: > Storing a fully charged lithium iron phosphate (LiFePO4) battery has a > minimal impact on its lifespan. In fact, it's recommended to fully charge > LiFePO4 batteries before storing them for long periods of time. These > batteries have a low self-discharge rate, typically losing 2% of their > charge per month. However, fully charged lithium-ion batteries can be > dangerous if left unused for long periods of time. > > On Fri, Apr 26, 2024 at 12:43 PM Forrest Christian (List Account) < > li...@packetflux.com> wrote: > >> >> >> On Fri, Apr 26, 2024, 1:02 PM Ken Hohhof <khoh...@kwom.com> wrote: >> >>> And I'm still using AGM batteries while all the cool kids are using >>> LiFePO4 with BCMs, so definitely don't listen to me. >>> >> >> The more I learn about lithium batteries, the more I feel that lithium >> has relatively few advantages for standby applications. >> >> My most recent knowledge acquisition is the fact that if you want to >> shorten the life of a lithium battery the best way to do so is to keep it >> fully charged. The higher the average state of charge, the shorter the >> life of the battery, although admitted there isn't much change in lifetime >> between about 20% and 80%. But keeping them at 100% isn't great. >> >> If you want to store a lithium battery without charging, it's best to >> drop the charge below 80% then store. >> >> In a standby application you really want to keep a battery at 100% which >> shortens it's life greatly. A better choice would be to keep it at 80% >> max but then you have other issues, not to mention the fact you now have to >> buy a bigger battery array. >> -- >> AF mailing list >> AF@af.afmug.com >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> > > > -- > Thank you, > > TJ Trout > Volt Broadband > 209.480.3122 Cell > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >
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