Battery discharging problem

I dropped my phone in a tub of water a month ago and didnt think much of it because it is suppose to be water resistant but then there was moisture inside the camera so I switched it off and put it in rice and the moisture was gone in a few days. When I turned it back on I noticed quicker battery usage and tried to optimise it or turn it off when not in use but the battery discharges even when powered off (about 15% in 6 hrs powered off). I sent it to samsung services and they just formatted and updated it then sent it back but the problem is still there. Long story short I think water went in and messed with the battery. What should I do? Should I send it again? Should I ask for changing the Battery?