How to Triple the Battery Life of AAA Flashlights

When using 3W LED flashlights powered by AAA batteries, you'll expect them to last for about 30 minutes. There's a way to triple the run time by using AA batteries, which I'll show you by hooking up an AA battery holder to it.

Step 1: Things Needed

Drill
Heat shrink tubing
Inexpensive flashlight to modify (e.g. Techlite Lumen Master)
3AA battery holder with cover
3 AA NiMH batteries
Wires
Wire cutters
Solder
Sandpaper

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 to hold the wires. This one fits AAA battery holders so that 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.