my sisters A1-811 just stopped charging recently, battery was totally drained too.
what i did was open it, i used my nail actually after watching a useful video on youtube, then just made sure the connections were in firmly (disconnected n reconnected the battery cable), and THEN i connected the tab to power, i think its the USB port thats messed coz it starts charging wen the cable is barely inside, like just wen it contacts the metal on the tablet...