My not that old Nokia 830 got slightly wet while near the coast the other day, after a large wave came up and splashed me ( don't ask) 
Anyway, although the phone is charging fine, and everything else seems fine, the battery is draining quicker than normal.  There was a tiny bit of water on the top of the battery when the phone was opened, although I am not sure how it got in, as the phone lives in a silicon case. Anyway, another thing I have noticed is that the time since last charge in the Battery Saver is showing 0 minutes all the time, even if it has come off the charger an hour or two earlier. 

So, could it just be that the battery is a bit stuffed, and if not, how much to repair the phone? A new phone is out of the question. 

Or if anyone from Microsoft is there and wants to send a guy a new phone for free, feel free. ;)