If I am at a base camp I tend to use my lamping battery, which is an 8"x2"x3" one with a 12v cigarette lighter on it, that keeps mobiles, iPods etc.. topped up for ages when used with a car USB adaptor.
I have been thinking about one of those smaller solar powered battery charger things for when I am out in the bush for days (as opposed to camping at meets N moots). I must look at the 2 ones mentioned.