a little lower tech than AFLM's (always well researched electronics recommendations)would be the Goal Zero 7w solar panel, with the Guide 10 pack, and an AC to miniUSB cord... the Guide 10 pack holds 4 AAs... can be charged with solar or miniUSB from AC, and is regular USB out....you could use rechargables like Eneloops or as a stand alone lithium pack without the charging capability...

the Guide 10 pack will take a charge from 12v via miniUSB, and the Goal Zero panel additionally has a 12v tubular out...