From what I have seen of the tablet opened on YouTube, there is no CMOS battery. It is all powered from the main battery.

I also worked on an RCA tablet and it had the same configuration, no CMOS only main battery. Really cheap!!

I tried to split the case but something in the middle kept the process from completing. Had a good hold on the keyboard. No screws on the back.

At some point it may not be cost effective to continue on this path.

Regards