Modifying lithium cell phone batteries?

I want to mod a mag with a 3 watt luxeon and a lithium ion battery pack. I want the light to be idiot proof - no worries about running the batteries too low or overcharging. I was thinking of modifying a cell phone battery pack and charger. If I was to take apart a cell phone battery, could I add a larger capacity (bare) li ion battery to the protection circuitry? Would it still protect the same way?

Probably not. Why don't you use a higher capacity pack to begin with, like maybe a camcorder pack.

It's a definite 'maybe'! The protection circuits I have played with appear to be configured for 1½ to 2C. If I put a two ohm load on a 7.2v pack, it either doesn't come on at all or only runs for a second before the protection circuit shuts it down. I can put a three ohm load on the pack, no problem.

I say go ahead and try it - as long as you have the protection circuit wired correctly, you won't destroy anything. If it works, fine. If not, you will just have the protection circuit kicking in too early.