This could be useful.
Per iLounge, Tekkeon has introduced its new TekCharge MP1580 battery pack for the iPod, iPhone, and other USB-charging devices. The MP1580 offers the ability to charge devices using between two and four AA batteries, and serves as a charging station for rechargeable NiMH or lithium cells. Other features include an inline voltage regulator to ensure safe charging, a built-in USB slot for connecting charging cables, and an external charge indicator.
The TekCharge MP1580 is available now and retails for US$25.