I have one (L0D, I think), it runs on the CR 123 batteries that Surefire does. Since I have an E1 Surefire as well, I feel the Fenix is a more versatile light, and fairly robust. More variation with lighting options, longer battery life, brighter. But, on hi power, the Fenix does heat up quite a bit, so the point where you could probably use it in a pinch to ward off some frostbite