is there a small, lightweight battery that runs at 12v? not a car battery... small and lightweight. (duracell and energizer .com do not tell me). i need to it power a computer fan... for the longest time posible. i was thinking one of those small looks like AA but smaller but on the websites it doesnt say the voltage and i'm too lazy to go check. what can i use to power the fan for awhile? (under a pound..)