If you updated to iOS 6 on your iPhone 4S or iPhone 4 and despite all our battery life tips, still aren't getting enough power to get you through the day, or if you simply travel and need to recharge on the go, the PowerSkin Battery Case for iPhone is worth a look. Like other battery cases, the PowerSkin fits snugly over your iPhone 4 or iPhone 4S -- sorry, no iPhone 5 version available yet! -- and hooks into the Dock connector to supply power.
Live at CES 2012, accessory maker Incipio shows us their next-generation Offgrid Pro case for iPhone. The big difference with the Offgrid Pro is that it has user-swappable batteries so that if you're going to be away from power for a really long time, you can back just as many 1700mAh cartridges as you need.
The Offgrid Pro will be available "soon", and will ship with two batteries, the charger, the case, and the band.