Ha yes, I've seen that video. That guy must be suicidal - I shudder to think how much cell reversal was going on there! One false move and he would have fried himself, at least he could have put insulating spacers between the batteries. It's another reason why I went for CR3032s, I don't know their short circuit current, but I'd be surprised if it is is more than a few 10's of mA (maximum recommended pulse drain is around 12mA). I haven't tried it because I'm also worried about cell reversal (and severe loss of capacity). The closest I got to frying myself was a minor belt off the rear of the BNC when I was fitting the end plate, (predictably) no worse than I used to get when playing with old 90V radio batteries and Neons.
I'm still wondering whether to include a current limiting resistor, say, 100k in series with the output. Obviously a fuse or PTC would be no use. The more I think about it, the more it seems like a sensible idea. It would drop the voltage into a 10M voltage divider, but not excessively, and I only want a rough measurement of leakage currents anyway.