There are a lot of mini-maglite hacks out there where people replace the bulb with a white LED. The only drawback is that white LEDs run on 3.3 volts, and 2 AAs only give 3 volts so the white LED runs dim. AntonOlson solved this problem by building a DC/DC converter in the shape of a AA battery that boosts a single battery to just about 3.3V, both of which go into the mini-maglight. – Link.
Battery shaped DC-DC switcher in a maglite