So, I have 5 banks of 4 paralleled 4S lipo packs, giving me 20Ah @ 74V nom. One bank was not balancing well, by that I mean, out of the 4S I'd get maybe .05V difference, sometimes .1V, even though I ran balance charging on that one bank several times.
OK, apparently I left the main power cutoff "ON" for maybe as much as a few days. The contactor was not on, nothing except the (analog) VM was in the circuit. I saw my VM was reading really low voltage, and after getting control of my panic attack I slapped my pack charger on it, and it came up to a reasonable voltage within minutes - around 60V. I then started charging each bank, and they all responded normally except for that one that had been giving me trouble. That pack would take a charge, then immediately the voltage would drop (stabilizing around 7V). I freaked again, and pulled that bank out, pulled out each battery pack and tried charging them individually... same result. All 4 packs in the bank were toast.
So, what happened?
My guess is that I had a bad pack within that bank, and it took the rest of the packs it was paralleled to down with it. Somehow having the main cutoff "ON" made this happen? Can someone explain this to me, in small words?