Small battery for wf

If you are trying to save weight, check out some of the 12V LiPo batteries that some Tag racers are using.

Comet has one on their website, but a local Rotax guy bought one from Amazon and it weighs around weight of two D-Cells or less.
Like Mike said If you want the absolute lightest battery possible the Lithium batteries can't be beat.
I have one in a hand held starter that i custom made.
They aren't cheap however.
Expect to spend from $100 to $150.00
Otherwise i have a very small sealed lead acid battery for $24.95
Go buy you a cheap drill with a li-ion battery and cut the handle from the drill to mount as desired. Then you have a charger and battery you can just swap out when needed.