I have some older Surefires, maybe 10 years old plus. I hadn't been using them much, but I recently tried popping a "dead" CR123 battery into a single CR123 SF body that had what I think is a 1 watt LED head. Anyway, the thing lit up bright as daylight and ran that way for probably another hour total, then started flickering very slightly, then dimming after about another 15 mins or so to a low level light that's perfect for getting up to pee at night, in which use it continued to run for about another 45 mins to an hour or so. So, a dead CR123 battery is not really "dead" until it's Surefire dead, which starts to make what I paid for the light originally seem like a pretty good deal. Now I can squeeze the last nano amp out of those batteries. My Inova single CR123 red LED flashlight also drains batteries completely, but it's longer than the SF light, and I don't always want to use a red LED light.

Edit: I just checked. It's the Surefire KL1 1 watt LED head and the E1E body.