iPhone 5S not charging EVEN AFTER replacing U2 IC?

I gave my Iphone 5S to a repairing guy who’s a friend of mine.

He doesn’t wanna buy new U2 IC, he has got few spare motherboards and he insists on removing the IC from them. Till date he has tried putting 4 such IC’s but no gain. I can buy new IC online and give it to him but he tells me not to do so, he will manage.

First of all he tested the charging port & ribbon which leads to the motherboard. That’s not the culprit. He is sure that the problem must be with the IC. But it’s been more than 50 DAYS since the phone is lying there, he still hasn’t come up with a solution.

I think that if I buy new IC online and give it to him, it will work.

Anyhow, my question:

1. Apart from the charging port & ribbon & IC, is there anything else responsible for charging the battery? I mean even if he puts new ribbon (with charging port) and U2 IC, is it possible that the battery still won’t charge?

2. What other solution do I have? Take it to official apple service center?