Last winter I built a 10s8p battery (sony VTC6) to replace a stock Evolve BGT battery. I swapped the Evolve ESC for a Unity, used a Bestech D140 charge only BMS, custom enclosure, and everything was running great.
Due to the size of the battery, even though I rode it a “decent amount”, I honestly probably never charged it more than a dozen times.
The last time I rode it, it was running oddly. It was stuttering and the battery reading on an LCD I had installed was showing it was very low even though I had just charged it. I tried charging the board and it was not charging to a full voltage before the charger would turn green on me indicating it was done.
I opened everything up and tested the voltage on each BMS wire and everything was good up to bank # 9. The 8 batteries in bank 9 had ZERO voltage…nothing.
Fast forward to now - I’ve done surgery to remove the bad bank of 8 batteries. Testing that pack alone still indicating absolutely no voltage at all. I disposed of them immediately since they were run down to zero, so I’m assuming permanently damaged. The remaining 9 banks of batteries all have a 4.2 voltage/ea.
My original thought was that I must have had a cell that went bad and brought down that pack. I wired 8 new batteries in place of the bad bank, thinking once I hook everything back up, the BMS would allow that pack to come up from 3.5 to 4.2 to match the rest of the batteries. It only charged for a couple of minutes and the charger turned green. Voltage on pack #9 is still only 3.5.
ALL this info to lead me to this question - was it not a bad cell, and is this just a bad BMS? I don’t see anything visually burned up on the BMS itself. It appears it’s just not allowing anything in bank #9 to be charged. The leads are run properly to the BMS and indicate the same voltages as if I probe the packs themselves, I just don’t know if there’s anything else I can do myself to test the BMS.
Also, if this was just a simple failure in the BMS, is there a better quality one I should be using? I went with Bestech because that seemed to be what everyone recommends, but I have a pretty big enclosure and can fit just about anything. I’m ok with spending more on a higher quality one if it means less potential of having to go through something like this again!