in the same boat as OP, looking for a way to keep my edge 305, MP3 player with same mini usb connector, and cellphone all charged on tour. I found an energi to go for my cellphone 75% off at target, at which point it cost less than the lithium batteries that came with it (and waaaay less than one of those damned mintyboosts). Unfortunately, that target didn't have the mini usb one, and the other target I went to still wanted $20 for it.

At this point I could solder together my own 2.5 mm (which the energi to go uses) to usb adapter cable, or just buy one of these guys, at 16$ shipped with every possible adapter the best value I've found in a 4AA solution:

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA:IT&ih=020

cons with the 4AA would be increased bulk, and not sure about the efficiency. 4AA=6v, and so I assume is reduced to 5v by burning off 1v with a resistor. Can anyone knowledgeable tell me which is going to be more efficient, that, or boosting 2AA at 3v to 5v with a capacitor?

And I've got a solar AA charger too, but does it ever f'n suck...