Incipio designed the case that protects your iPhone 4/4S while maintaining the long lasting life of the battery. The offGRID™ PRO case is in fact a battery backup case that will never let your iPhone down.
The case is made from durable plycarbonate. Though it maintains the slim profile of the iPhone, it changes a little the aspect of the back side due to the dock connector for the additional battery. offGRID™ PRO offers two interchangeable and rechargeable lithium-ion polymer batteries with 1600mAh capacities each. You can easy install the case and remove the batteries.
Your iPhone starts charging only with a single press of a button. Pressing more insistently will display the battery status. Four blue LED light indicate the life of the backup battery. The case gets charged in no time via an external charger. Also, it comes with a 3 ft (0.91 m) Micro USB Cable and a 3.5 mm Headphone Extender.
You can get your offGRID™ PRO backup battery case for $99.99 from Incipio.