Interesting... That would require batteries that have been pre-modified (or having to modify them). Much simpler (low tech) than trying to sense the chemistry of the battery though. A simple continuity check could then test to see if the bottom is exposed. Of course if someone were to do this to an alkaline we're back into the original problem - chance for explosion/rupture of the cell.

I managed to find a few links to manufacturers of charge management ICs but I haven't looked closely enough at the various datasheets to find out if they can detect between the different battery chemistries.

Bruno