im seeing a lot more of this issue on the iphone 7 and 7 plus im starting to think its a signature issue with them I restored one and started working fine for 5 minutes and the same thing happened. It has some issue with the audio if you have warranty take it to apple and get it swapped out if not contact ipad rehab or sts telecom.
this is most likely due to a cheap after market screen try a original screen on it. also with the new ios update a lot of people are having issues with the phones even with original screens this effects the 8 8plus and X but me myself have not had any issues yet. I hope this was helpful if you have anymore questions please feel free
How did you disconnect the battery and the charging port from the board? Did you use metal tools? Did you maybe go to deep and knocked something out of place? Have you tried putting the old battery back in? It can be a lot of things if you have a microscope look at the board o have customers sending in phones everyday to us because they did something wrong while changing something on the phone.
it may be because some kind of pressure was applied to it if you didn't drop it. of when they refurbished it they may have left something small such as a small piece of glass and when the smallest pressure cracked it.
have you checked ebay? this is what I found check it out see if it works for you! https://www.ebay.com/itm/GENUINE-ACER-ICONIA-A501-A500-10-1-TABLET-DOCKING-PORT-BOARD-CABLE-LS-6874P/182036732618?epid=1200248896&hash=...
I hope you still have the original home button! the 7 will not work with any other home button each button is unique to the phone. if you have the original home button try it on another new screen because sometimes the connector on the screen is bad. hopefully you haven't damaged your home button flex.