For my headlight I use a regular flashlight, fixed to the handlebars with interlocked hose clamps. It takes two 18650 batteries. I recently bought a similar flashlight that uses only one 18650 battery. They both have the same CREE LEDs (XML T6).

I've never been a whiz at electronics. Does the fact that one of the lights uses two batteries mean that it should be brighter? Or that a full charge should last longer? I gave a try shining both batteries in my dark garage, and the brightness seemed about the same (2-battery one maybe having a little edge).