Odds are the motherboard did take damage. The battery itself should not really be harmed by the water, but possibly the contacts are corroded. Typically water damage will effect the motherboard and it can take out random things which may or may not be immediately noticeable. They can even be very small things. I would follow the motherboard guide to take everything apart. Take a look at the battery and its connections. If you see any buildup on the battery possibly replacing it would work, but doubtful honestly. Look over the motherboard to see if there are any water stains which should look like very faint white circles on the board. If you see these you will want to replace the motherboard if the issue is of great concern to you. Otherwise you can just continue to use it until it with your problem until it dies out.