If you are under warranty, simply e-mail them or call them and tell them something is wrong with your light but your not sure what, but ever since it was new it never would stay lit on high for more than 55 minutes (or whatever minutes it is), but the specs say 2 hours. They'll do one of two things, either send you a new set of bats or entirely new light with new bats, they sent me an entirely new light. They will of course want the old light or bats returned after they send you the new stuff.

Don't tell them you suspect the bats, act like you don't know anything and let them decide to make whatever decision they want.