iPhone 6 not turning on - tried almost everything

Hey iFixit Team,

I purchased an iPhone 6 which was not turning on. It had a cracked screen and once opening up I could tell the battery had been replaced.

I replaced the battery and screen with genuine parts from an iCloud locked iPhone 6. I got the phone turning on but it was running slightly hot and draining faster than normal.

I restored the software from recovery mode and the problem persisted. Now the phone does not turn on after I left it dead for a while. I know I could probably get it to turn on if I put a charged battery in but I would like to fix the root cause. I have a feeling it might be a motherboard issue but would like to seek clarification and advice...

I have careful performed the screen replacement and reinstalled the battery with the proper apple adhesive strips so I should be able to get a replacement from apple if I can't get it fixed.

Thanks again,

Nick