damaged U4500 or what else?

So the phone was originally bought in Germany by my GF Father. It was a little bent, had few missing screws, and sometimes touch didn’t work. I fixed the bent case and replaced the screen a few times (She just dropped it few times with fatal damage to screen).

The problem really began when I ordered missing screws and put them back into phone. She told me that It didn’t charge at all. I checked the charger first but it was ok, so I proceeded to look at the phone. For the first few times trying to charge It, It showed in exchange charging,and then not charging. I reassembled It about two times(mainly deassembling only to screen connection cables where were missing screws on the shield ), and after second time it charged to 78% in maybe 15 minutes and then stopped. Since then It reboots after few minutes of doing completely nothing, doesn’t charge up at all. After reboot, for a few seconds it shows 1% and then hits up to 78% and stays there even after rebooting probably 30 times since then. Selfie camera died too after adding missing screws but don’t know if it changes anything.

Any ideas? I replaced the bottom part which contains charging port,minijack etc - with no result. I read about that U4500 chip. It seems to be quite cheap but I will have to practice with my HotAir for a bit to do this kind of action, and at this point i have no guarantee that thats the problem. If i have done some grammar mistakes, please forgive me - It’s not my native language.

Best regards,