I use a 4000mah Geshi Ace 2S Lipo Pack which I got together with a second hand kit. I'm not sure what happened why it doesnt want to charge anymore but here's what went down:

The battery's balancer plug (the 2 black wires and 1 red wire) the red wire got disconnected from the plug while I was removing the lipo low voltage alarm from the pack (so I put it back - just a quick fix super glued the wire back on the leads).

The next day, I continued using the pack without charging cause the low voltage alarm showed all green lights. After around 30 minutes, the low voltage alarm went off on one of the cells so I tried charging it but the charger says there's a problem - it says one of the cells is 0V and the other one is 3.8V.

Did I discharge it completely? Or is it just a problem with the balancer plug?

Or did I just get an old pack that needs to be replaced already? It's probably less than a year old but more than 6 months (used in drift competitions from what I know)- how long do lipo batts last anyway?

Should I buy a new one or try re-soldering the wires on the balancer plug?

Help please!