this one, the battery is 4 18650's shrunkwrap. I figure if they crap out, I hit up Battery Junction, and get 4 more chinee 18650s, and rebuild the pack. catch-22, those batteries cost nearly as much as the light :huh p.s. 9:42, and its STILL running, so thats 3.5 hours so far. I think I'll shut this down and give the batteries a break so, when it goes to blue, you've got at least 2.5 hours left when it flashes and goes to red, you've got at least 1:45 left when it flashes again and the red starts blinking, you've got at least a half hour left on high. !!!