Battery failed after water damage

It is likely that the battery power lines on the motherboard have developed faults from the water or it could be just the battery itself has shorted. It will need checking over by a knowledgeable technician to diagnose if there are any voltage issues one the board. It would probably be a good idea to change out the battery anyway just in case the battery has also become faulty. Corrosion can also be a factor in the long term so getting the board properly cleaned can be also put into the equation.

From the sounds of it your system got quite wet, it’s likely the logic board sustained damage.

I would start off carefully inspecting the logic board for damages components as well as corrosion damage on both side of the logic board, I would also look at the inside surfaces for staining as that can point to where the spill effected.

I would hold off replacing the battery until the damage is repaired as that could lead to more serious damage.

It might be wise to seek out a Mac repair expert as this will likely require logic board component replacement.