The BMC cable which connects the battery to the logic board is the data link between them so the charging logic knows what is the batteries status.
Clearly your logic board got wet and has shorted out something. At this point you need to pull the board and do a very detailed inspection for wet areas and/or damaged components. Fixing this system will require deeper skills and tools are you able to repair micro-electronics? It might be best to find someone who has these deeper skills as liquid damage systems are one of the hardest to repair.