My Tab S 10.5 screen had a similar problem. When charging cord is inserted it showed a low charge, 3%, and would not go beyond that even after changing the adapter and the USB cord. If the charging cable was disconnected the tablet would automatically power itself off because of low charge. After watching several YouTube videos I decided to take the back off and unplug the battery as suggested. However, before that I powered down the tablet. It then automatically powered back on by itself and the charge indicated 100%. So apparently it had to be rebooted to show the correct charge. Problem solved.