Battery problems after front panel replacement

I recently helped my friend replace her iPhone 6 front panel. Afterwards, the front panel did not power on, so I followed the guide on resetting the battery (having read that that is the solution) and got her phone up and running again.

Afterwards, she let me know that her phone's battery is draining irregularly fast, so she gave it to me to try to fix again, and I noticed that not only does it drain very fast, but it also charges very fast (0% to 100% in less than 2 hours).

Sounds like I damaged something while doing the repair. Does anybody have any insight into what could be the problem and/or what could be the fix?

Greatly appreciate any advice. Thanks!