A friend of mine has an odd hobby. He builds custom flashlights! It is a whole sub culture that I never knew existed. He polishes the lenses, machines the bodies, and tweaks the chips in them. So far I have bought 2 from him. They both use 2900mAh rechargeable batteries. The smaller one uses 1 and has 1 LED and the larger one uses 4 batteries and has 3 LEDs. They both have multiple modes...low, med, and turbo! The smaller one has 1200 lumens and the larger one has around 3600 lumens. It is just stupid how bright the big one is! It has a safety shut off otherwise it will over heat.