Issues after housing replacement

I changed the housing along with a new lcd on my iPhone 6s plus.

When I turn it on. It sometimes works and sometimes doesn't prompting the plug in charger icon. But oddly it will actually turn on sometimes and after a 10 - 20 seconds will shutdown with no notice.

Does this mean the battery has been damaged during housing replacement.

Secondly the antenna on the top left wasn't coming off as I didn't know about the hidden screw under sticker and I ripped it off.

Now the little plate on the back has broken off but I sandwiched it back and screwed it down. Should I replace with new one?

ok switched battery and now problem solved.

i have a new issue now. The volume button randomly presses itself especially the vibrate rocker? does the flex for volume need to be changed?