Juice Pack Helium for iPhone 5
Double the life of your iPhone 5 with the Juice Pack Helium, a tiny, ultra thin, 1500mAh iPhone 5 case and battery extender. It's a case, a battery, it also enhances the sound by bouncing it towards you! You can charge the Juice Pack and the iPhone at the same time with the supplied microUSB, and it has four LED indicators on the back for checking the battery status AND an on/off switch.
You can also get the Juice Pack for the iPhone 4/4S here