Motherboard overheating when phone is off, and battery connected.

My phone received seawater leakage. I turned it off as soon I could, let it dry overnight and opened it up the next morning. I found lots of dry salt (Looked like a layer of white powders.) I cleaned it up with 90% Isopropyl alcohol, and removed thicker layers of dry salt with a plastic pick. Now the motherboard overheats when I plug the battery connector in. Is this normal? Or should the motherboard only heat up when I power the phone on. Does the motherboard still have a short on it? Or is it a battery issue?

Thanks in advance.

Before and after images from cleaning: