well, don't bother hacking open an Energizer Lithium 9 volt. I just opened one (machete) and there were 3 rectangular plastic cells (and a sweet puff of gas, cyanide?) -- not metal cylindrical ones like in the alkaline 9 volt -- (hope it didn't kill any brain cells I really need..)
Just a followup - I've had the batonlight for several weeks now - and because it's on my keychain - not a day has gone by that it didn't get used. It's amazing, really, to think that a product would be so useful and yet so inexpensive.
Granted - it's not the brightest, or the best color rendering, or the tightest beam, but it's always with me - and that's the value of this light. You don't leave your keys, and you don't leave your light.