Flashlight that can operate with alternative size batteries

Various embodiments of a flashlight are provided. In one representative embodiment a flashlight includes a light source, a housing and at least two battery locations inside the housing. Each battery location inside the housing can accommodate at least one of at least two batteries, each of which can be a different size. The flashlight also includes an electro-mechanical structure that prevents a closing of an electrical circuit that electrically couples the batteries to the light source, when one of the at least two batteries in the flashlight is a different size than another.