vadikb said:
Yeah this happened suddenly after a year of use. If the BMS stuck on balancer, will connecting a new smart BMS balance the batteries automatically or do I still need to get those batteries out of that group and charge them manually to match the voltage with other groups?
Neither. They are damaged and a fire risk. You need to replace them.
If you don't, you can't predict what will happen or when, and they may burst into flame at any moment once recharged, either during charge, during use, or even just sitting there.
They may, of course, do nothing other than perform much worse than they originally did, lowering the capacity and performance of the pack, but I would think that any risk of fire would be unacceptable.
If it's not unacceptable to you and you intend to recharge the cells, then please make sure you never use or store the pack anywhere near other people or animals who may be injured or killed if it does burst into flame.
If you can see the balancing resistors and transistors on the BMS board (some are covered in goop and essentially untestable), then you can test the BMS for leakage at the balance wire by disconnecting the balance wire from that cell group (or just unplug the entire balance connector from the cells).
Find the balance resistor that leads to that wire. There will then be a transistor with one of it's leads connected to the other end of that resistor. That lead you don't test; it would just read the reisstance of the balancer, which is unimportant.
Then set your multimeter to 2kohms. Place the black meter lead on the disconnected end of that balance wire, and the red meter lead on one of the other two leads of the transistor of that balancer. It should read "open circuit". If it reads anything else, go to the next lead of that transistor. It should read open circuit.
If you get a reading on either one that is essentially the same as the balancer resistor's resistance, it means that transistor is stuck on, and you need a new BMS and new cells.
If it reads open circuit, it's not stuck on, and you probably don't need a new BMS, just new cells.
Example of the kind of parts arrangement you're looking for is below; every BMS is a little different.