That's one of the things I really like about the Protege (and other similar mods), if there is ever the need I can just grab one of the many 510 batteries I have lying around, not that I've had the need. I tried just for kicks, and it was pretty wimpy feeling, but it will work if I need it to.
I also like that it really is a very simple and well designed device, there is very little to go wrong, at worst I could see myself dropping it and breaking the switch, but that is easily replaceable. This is my first mod, and I'm loving it.