(tl;dr version at bottom)
Well, I had a Samsung Captivate Glide. Worked perfectly. Fast, 4G, you know the deal. Anyways, the screen broke, so I browsed around on ebay. I found one on ebay for $80 because the the 4 touch buttons on the bottom of the front screen didnt work.

Well, it arrived in the mail, and it's water-damaged. The phone freezes for a few seconds EVERY time after you unlock it (slide the lock screen off the display or using a pattern). The lock screen image will freeze for about 5 seconds before unlocking the phone. Additionally, the touch screen will act as if you are long-pressing whenever you just tap something on the screen. However, this only happens if you haven't touched the screen within a few seconds (about 7-10).

Now, here's where it gets weird. I swapped out the perfectly-working mobo from my old phone into the new, water-damaged one. Absolutely no change. I tried re-flashing and restoring both mobo's to factory settings.

Here's where it gets extra weird. The phone acts COMPLETELY fine when it has less than 10% battery. No freezes. No false long-holds. Nothing. It works like it's supposed to. If I start charging it or if it's above 10%, it starts messing up again.

Any idea on what the hell to do? I'd rather work with what I have if possible.

TL;DR: phone freezes and ****s up a lot, unless it's less than 10% battery, in which case it operates perfectly. Water damaged. Have spare parts for everything, except for screen. Tried re-re-flashing, restoring to factory settings, and swapping out the mobo.