When using 3 watt LED flashlights powered by AAA batteries, they last for about 30 minutes. There is a way to triple the run time by using AA batteries. In this Instructable, I will show you how to hook up a AA battery holder to a flashlight.
Step 1: Things Needed
Heat shrink tubing
Inexpensive flashlight to modify (eg. Techlite Lumen Master)
3AA battery holder with cover
3 AA NiMH batteries
Step 2: Extended Battery Pack
To connect wires to the flashlight, drill a small hole onto the body and sand the edges. Cut the wires slightly longer than you need and solder them to the flashlight's battery holder and the AA battery holder. For my flashlight, the wires were long enough to reach my pockets. Heat shrink tubing can be used to cover the solder joints. To make it water resistant, add hot glue to the drilled hole.
If it doesn't come with a battery holder, you can make an adapter instead to hold the wires. This one fits AA battery holders so you may want wider dowels. To make the extended battery pack detachable, you may use 9V battery clips or DC power connectors.
Note that in the photos, I sawed the aluminum body.
Step 3: Helmet Mount
To mount the flashlight to a helmet, elastic bands or bungee cords may be used. Now your flashlight will run for a long time!