Running off 4 standard NiMH rechargeables you can get 2hrs @ 200lumens, 4hrs @ 100lumens and 8hrs @ 50 lumens. There are also 2 different flashing modes and a strobe mode.
The battery packs attach with a velcro strap to the stem. I bought a few extra battery holders so I can swap in fresh batteries very quickly. The white button on the rear turns the lights on/off and switches between power levels.