http://www.amazon.com/Nirve-Vintage-.../dp/B000QFOMJY

I purchased two of these not too long ago. One went on my cruiser, the other on the ex's (sigh) cruiser. They are powered by 9v batteries. I ride quite a bit in evenings, and have noticed solid battery life. My one major complaint is that after riding around a bit with the light mounted, the system that switches between "hi, "low," and "both" beams is loose. When I say loose, I mean that the points on the switch that select between modes are finicky. I ended up doing a small DIY mod to fix the issue...as I'm sure you could do also.

Enjoy.