ships from china, but its cheap and has a good review here:
Charge the Power Case by USB cable. Plug the power station to charge your iPhone 5 at any time and any where. To charge the phone, simply slide in the phone into the portable battery and slide ON-OFF switch to on.
Recharge iPhone 5 On the Go
2000mAh High Power Capacity
Lightweight and Protective
With Battery Power Indicator
Emergency Power Pack:
Input Voltage: 5V
Input Current: 500mAh
Output Current: 500mAh
Charging Time: 5 hours
Size: 135mm(L) x 61mm(W)x 16mm(T)
* Please Charge the Battery Case before Usage.
* Please Charge the Battery Case and iPhone 5 Separately. (Do Not Charge the Battery Case and iPhone 5 At the Same Time)