I had this same issue and apparently all connections are snap on and the charge port connection was not properly seated and would cause random restarts and charge issues. Would state fully charged and then power off and restart and show a different charge level…
I opened it up and found that the connection was just laying there barely making contact and at times not making contact at all. I didnt need a new battery or Board. Works like new and my girlfriend says its the fastest tablet she has used. Hope this helps someone fix there tablet without spending more money.