We have featured a few of these Mophie battery cases for the iPhone and iPod before here at Geeky Gadgets, the latest one is for the fourth generation iPod Touch and it is now available.
The Mophie Juice Pack Air for the iPod Touch 4G, according to the manufacturer will give you almost double the battery life on your iPod Touch.
The Mophie Juice Pack Air for the iPod Touch 4G is available in a range of different colors, which include, red, blue and black, if you want one they are available for $49.95 from Mophie.