Strange charging issue, stuck on Apple logo!

Hiya,

I’ve got a customers’ iPhone here that’s give my me a bit of a headache. The customer came with a damaged charging port and a draining battery. The phone being now old, I didn’t questionned his draining issue before hand.

The customer is on his 3rd visit to our store, initially replaced charging port flex and battery, 2nd time I replaced the battery again assuming it could be a faulty battery (the phone was hanging on Apple logo then switch off).

On his third visit, today, I kept the battery in and just plugged it on charge (with a usb volt/amp meter, the phone was taking its full amp ) the phone kept restarting for 15 minutes then switched on with 2% battery. It is now charging fine, until the battery fully drains. Then the problem comes back.

UPDATE : The phone also restarts randomly when trying to drain the battery.

(I’ve also tried another charging port flex, which hasn’t helped )

Would any of you guys have any suggestions on this repair ?

Thank you !