I have a pannier set up on my bike, which allows me to carry a 12 volt, 6 amp-hour sealed lead acid battery (it is smaller than you might think). This powers my homemade FIFTY WATT HALOGEN HEADLIGHT.

It is more powerful than my mom's '00 Honda Accord's headlights (we recently sold that car - *cry*).

Yeah. It boils water, so watch out.