iPhone won't charge after replacing battery and charge port?

Hi

After replacing the battery twice and the charge port once the iPhone won't charge at all. I keep having to charge the battery externally.

When plugged in it says charging as the logo comes up and itunes recognizes it.

Somebody said it could be the charging IC, I found one to buy but don't know if it would be easy to fit?

Some help on this problem would be really really appreciated.

Another thing, when fully shut down the iPhone stays warm which drains the battery. Maybe these are related?

Thanks in advance!