Just as a reference point for how these charge: I knocked together a USB charger tonight by cutting the tiny Nokia barrel plug off a cheap aftermarket charger I bought (does anybody have a decent source for these plugs?), and chopped the end off a USB cable (doesn't really matter which type, A-B, A-Mini A, etc), then soldered the USB red to positive on the plug, USB black to the negative of the barrel plug, and cut off the green & white from the USB side. Shrink wrap the joints, and you're done. Just be careful to note that the outside (barrel) of the nokia plug is negative, and inside (tip) is positive.

The charger seems to work from the USB port on a PC, a 4AA battery NiMH pack that I put a USB socket on, and the AC-USB and 12V-USB adapers that came with my Holux GPSSlim 236. Should be a very handy charging solution, but unlike the boxwave noted above, this is for power only, not data.