iPhone 7 keeps restarting and does not show battery health

I was given iPhone 7 32GB for free and it had screen smashed. So I changed the screen and while I opened it, I changed battery too. When I started using the phone, it always restarted when trying to log in to my Apple ID or updating the phone. Battery did recharge to 100% ok. Yet, phone does not show battery health and keeps searching it.

So I thought maybe the battery is faulty. I changed again a new battery and phone keeps restarting if I try to log in to my Apple ID or update it. Battery does not show health and this time it won’t charge more that 27%.

All I can do is perhaps change a charging port. I don’t know the history of the phone and I don’t know how to check or fix problems on board.

Any advises or should I just toss this to trash bin?