Normally device reboots when Maemo finds bad process or can't start some process so OS starts reboot the device to start it. (It is weird method of starting bad processes, especially if it doesn't help and tablet keeps rebooting).
So what can you do is enable R&D mode with flasher utility: flasher-3.5 --enable-rd-mode --set-rd-flags=no-lifeguard-reset -R

But if you have problems with battery it will not help... You should replace the battery.