I have this (graphical) tablet for a long time, and when I started working at BUT_ I found out we have the exact same model here too. But it was not functional. I thought thoroughly for a while and then searched for Genius disassembly videos. None found with this exact tag but the procedure of removing the batery from the tablet’s ‚pen can be seen in the video after the break (0:35).

Just pull from the oposite side from the tip and voila, so simple.