Do this:
Walk into an ATT repair/warranty center. Tell them that if you leave your phone on the charger over night, the device shuts down after fully charging, and you borrowed a third party battery and the behavior didn't persist.
New battery, boom.
Regards
Smith
Just to add, I've done this 2 times. They also gave me the option of a new captivate each time lol, so I took it xD
