iPhone 5s Not Displaying Correct Battery Percentage

Hi,

I have a friend whose daughters iPhone got some light water damage, It was from what I can indicate very little if any water as no water indicator stickers were activated. I had pulled the phone apart in which it did have some water spots on the top of the battery so I thought to be on the safe side we replaced the battery. The phone did turn off when it was wet however, it remained off until I was able to inspect it and clean with pure alcohol.

When I replaced the battery phone turned on phone and all was working fine all expect the battery percentage, It shows a percentage, for example, 39% when not on charge but when on charge it will go back to 30%. Then when you restart the phone I guess it comes up with the correct charge. I have also replaced the charging point in which had no result. Other than this issue the phone works perfectly fine,

Just wondering has anyone else had these issues before? I know it can only take the littlest amount of water to do so much damage so I'm leaning towards it being a main board issue next?