I have since opened the pack and after disconnecting the balance lead connector I got to a point where I could measure the cell groups individually. So I get a reading of 3,4 or 3,5 on all of them but one shows only 3,2.
Also, when this balance connector with 14 cables in total(13s pack) is disconnected the battery shows its normal 43 volts when checking the main negative and positive.
Kind of stange huh. When BMS is connected shows only 37 volts but disconnected I get the accurate reading of 43 volts.
I guess maybe the BMS has tripped or something? Or.. I just need to balance the cell groups and then connect the balance lead connector back into the BMS again?
But how can I do this without dissassembling the pack? Is there some kind of 13s-balance tool I could order? Where you just plug it into the balance lead connector and it balances all the cell groups this way? Before it is put back into the BMS.