If you read too much about lithium batteries it just makes you paranoid!
I am not a chemist, so take this with a grain bag of salt, but from what I read I understand that lifepo4 and NMC batteries have a calendar life, which is negatively affected by storage at higher states of charge and higher temperatures but also a cycle life which is negatively affected by charging to higher voltage and discharging to lower voltage. and of course number of charge cycles. What constitutes a charge cycle is hard to pin down. 100% to 0 would definitely be one, but 70-30, then 90-50, then 65-36, etc.? I imagine 100%-0% counts as 1, but does 70-30 counts as .4 of a cycle? I doubt it’s linear and likely only quantifiable by extensive testing and only valid for that battery types size etc.
The thing that makes me paranoid is that I read somewhere that if current is pushed into a lithium battery, even a tiny current, even if the voltage doesn’t go very high, if done long enough, it will overcharge and ruin the battery. That is to say there is no safe “float” voltage. Once charged, stop charging until some energy has been used. So it seems to me that traction use, where the battery is charged then disconnected and used, is a simpler situation, but solar charging must be setup carefully so as to not hold the batteries at a high state of charge.
I have decided that the best policy is to avoid holding at high voltage ever, but just use as necessary and convenient and not worry too much. Have a large enough battery that you don’t have to use 100% of its capacity every day.
With lifepo4, if not held at high voltage with solar, service life should be decades if rarely drawn down below 20%.
anton
The thing that makes me paranoid is that I read somewhere that if current is pushed into a lithium battery, even a tiny current, even if the voltage doesn’t go very high, if done long enough, it will overcharge and ruin the battery. That is to say there is no safe “float” voltage. Once charged, stop charging until some energy has been used. So it seems to me that traction use, where the battery is charged then disconnected and used, is a simpler situation, but solar charging must be setup carefully so as to not hold the batteries at a high state of charge.
I have decided that the best policy is to avoid holding at high voltage ever, but just use as necessary and convenient and not worry too much. Have a large enough battery that you don’t have to use 100% of its capacity every day.
With lifepo4, if not held at high voltage with solar, service life should be decades if rarely drawn down below 20%.
anton
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