Introducing offGRID Battery Pack for iPhone 4

Incipio has announced a battery backup for when the iPhone 4."Promising to double the life of the battery in your iPhone 4, the off-grid power solution is a portable all in one case. Weighing just two ounces and a thickness of 6 mm only. "

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http://www.myincipio.com/iphone-4-battery-case/