One of those modding articles discusses how to reprogram the UPS's battery manager with numbers suited to LiFePo4. A bit iffy, that; who's validated those values?
Most of the packaged-up drop-in replacement lead acid to LiFePO4 batteries I am seeing aren't just a group of raw cells, but have a battery management system internally. Even the least expensive should be able to protect the cells from overcharging without modification to the UPS.
From what I read, it's not the overcharging or the charging that is the issue, it's the cutoff voltage at which a lifepo might be harmed being a higher threshold than a lead acid battery, so you have to have a BMS for the lifepo which increases the cost and can cause the ups system to miscalculate runtime as it may cut off when it thinks it has 10% remaining.
But if there is a hack to recalibrate them, then great. I'll do some searching for it now as I have two little bms's that need batteries.
