Why is my battery getting so hot its shuttin device down after a new

Hi Deb. My initial thought is that the soldering of the battery connectors may not have been successful. Too much heat applied could damage the battery flex cable (causing a partial short) or damaging the logic board.

I would open up the device and do a thorough visual inspection of the battery connector area.

It is also possible that you received a bad battery. If you are confident in your soldering skills, then you could put back the old battery to see if the excess heats goes away.