BMS empties single cell in a battery pack

I built 1P10S battery pack using Samsung INR21700-30T (from And this BMS (35A with Balance).

First time charging battery reached 40.4V. This seemed odd, so I disconnected the balance connector and measured individual cell voltages first 3 were 4.2V, 4th was 2.6V and rest were also 4.2V. Ok maybe the first charge is just wired I thought and manually charged that cell using 1S charger to 4.2V, reconnected the balance connector. Just to find out after few days same thing happened. Charging from battery charger doesn’t seem do charge that cell (falls back to 2.6V if it even manages to charge a little)

After manually charging that cell I tested it for 1km and pack as whole works.

As far as battery pack is well build (all cells are isolated from one another, none of the balance wires cross each other,…).

I suspect faulty BMS or that cell (I will recharge it and check if it discharges without BMS connected)

Did anyone experience something like this (and what was the issue)?

Hi! You can measure if any current runs over the balancing-lead that goes from/to the cell to see if there is something strange going on there. Also normally when a BMS is balancing a cellpack that resistor will get hot (located on the BMS)

The link is broken. What BMS?

If it’s Bestech, I’ve had faulty ones.

After almost a month all cells (removed BMS) seem to have the same voltage

1 Like this is the BMS in question

1 Like