well someone PLEASE correct me if i am wrong, but, your amp hours are just how much power is contained in the battery. now, all you really need is to change the voltage and your USB device should be powered just fine and draw what power is needed. what i suggest (this is just what some crazy student thinks who wants to help): voltage regulator, fuse, thats it. as for your solar panels, what is your amperage going in? with a charge time of that long, i think you could be safe with a larger amperage