I've had instances of some users holstering thier berry the wrong way, ie. facing outside in the holster thereby unknowingly pressing some of the keys and prematurely draining the battery in doing so. I'm guessing your berry is holstered correctly ;) I would change the backlight to 10 sec. and see if it stays on longer than that (w/o pressing anything else of course), this would be a good starting point in troubleshooting whether or not something else may be wrong...
hope this helps
