Phone will not power on

So I’m a tech savvy individual I have repaired lots of Iphones and androids but this one has me stumped.

Received it from a friend, was able to turn it on and perform a factory reset, then was able to get to the main screen, did the screen test and it passed then the phone randomly turned off, so I plugged it in and let it charge (He hasn’t used it in like 2 months so I thought it just needed a fresh charge) after leaving it plugged in over night, it still will not show any life, I opened it up, no water damage and no physical damage anywhere to be found I also checked all of the connectors and they’re in excellent condition. Also no battery swelling or punctures. I have tried 8 different cables, and no dice, I’ve tried the soft reset, and a few other methods, pc won’t detect it, so I’m not sure how to go about. Any advice or anything of the sorts would be swell. Thank you.