I charge from a USB type car plug all the time.
But I do use my iGo cable and tip.
The iGo charge anywhere is both a wall charger and it has a battery pack inside. I can get at least two charges of my reader off the internal battery. And with an adapter can be charged from any wall outlet (100 - 240 volts) -
http://www.igo.com/mobile-devices/ch...t/ps002730001/
They also make a device that uses 2 x AA batteries.
http://www.igo.com/powerxtender-char...t/ps002640004/
Carry a handful of AA batteries and you are good to go even without a wall outlet.