This amazingly powerful pocket light is only 4-1/2" long, yet is as bright as a 4 D cell flashlight. The E2 features a hard anodized aluminum housing with a Pyrex lens and a steel pocket clip. Twist the flashlight for constant light, or depress the tailcap for momentary illumination. The tailcap also features a locking device to avoid accidental activation. The E2 comes complete with 2 lithium batteries that have a 10 year shelf life.