After watching Systm Episode 86, I decided to build the second version of the USB Battery Pack. This is, as David has pointed out, not the best way of charging a USB device, as it simply relies on a 7805 Voltage Regulator. But I had one lying around, so I decided to go with this version.
I used an altoids-maxi-tin, which left me with enough space to fit an iPod cable in as well.
