Phone heating up and battery drainage

Overheating is always related to a short to ground..any other issue such as freezing has to be viewed as a consequence of it before the short has been taken care of. In the top right you have the camera, try disconnecting it and see if overheating disappears. If not try booting the phone without screen and other parts plugged on the logic board and if overheating disappears reconnect one by one to isolate the fault. If you still have the issue with the naked logic board, it might have been damaged incidentally during repair, if you have a microscope check connectors and close components to try and get some hints.