Irrational Battery after Screen/Display Change

Hi there,

I changed the broken display of my iPhone 6s and ever since then it behaves irrational. The battery is drained completely after less then 4 hours of use. Sometimes, after fully loading the phone, I unplug the power chord - start up a program and the display goes dark with the "load battery" animation. Then it shuts down. After some seconds you can power it up again with the power button and it will work just fine with showing full capacity on the battery.

I already reopend the phone and checked all the connections. Nothing to be seen.

On a side note: the back side on the top, around the camera modul tends to get a little warm, well warmer than my hand. You can feel the warmth.

It is not an ifixit replacement display since ifixit could not deliver when I needed one ...