I've got a setup with 32 LiFePo4 batteries, 280Ahr each, that have been sitting for a couple of years. Most of them are at a voltage of exactly 3.32v, but three of them are lagging behind at 3.28v. Do I need to do anything special before I install them into a battery management system (BMS) for this system? Is it okay to use a Li-ion charger to bring up the charge even though it goes up to 3.6v and I can't control the final voltage?
2 Answers
Generally, the best practice is to fully charge each individual cell first. Once they’re charged, connect them all in parallel and let them balance for a couple of days before building your final battery pack. This helps ensure everything runs smoothly in the long run.
If your BMS has an active balancer, you can just connect them, charge them up, and let it handle the balancing. Alternatively, you could put all the cells in parallel and let them sit for a few days to equalize. Of course, if you're keen on getting all three of those lower cells up to 3.32v first, that's an option too, but it really depends on how much effort you want to put into it.
That's true, but some balancers can be pretty slow. I have one that uses a 1A balancer, and it took two days of consistent charging just to balance everything out. Still easier than connecting them all in parallel and hoping for the best.
Yeah, I hear you! I prefer to be efficient too. My dad doesn’t buy that either.
I get that, but does a 40mV difference on just three out of 32 batteries really matter if the BMS has taps for each one? Bringing those three up to 3.32v seems tedious, and the parallel method feels risky.