usb host mode (usb battery)

[wcoolnet at gmail.com (William)]

I want to use USB host mode on my 770 and am looking for a portable 5V 
power source.
Right now I'm not sure if I want to build one my self with a 9V battery 
and regulator or buy something.

Any experience with the "Swiss Gear Portable Battery Charger for iPod"?
http://www.geeks.com/details.asp?invtid=GA-6227-15F00&cat=MP3

or similar?
-William