50g Backup Battery

[Vtile]

Yes the above. The backup battery circuit is extremely simple what I can remember... IIRC it was parallel with main batteries, not separate island powering memory chips (if any) only.

I suggest to use good quality modern "ready to use" NiMH cells, in your device if it is not a daily user. Those should be less prone to leakage than alkaline cells (which always leak when they are fully empty and chemicals start to eat the seals and body).