TestFreaks posted a review on the Juice Pack Air for iPhone 4

Mophie was one of the first companies to develop and market an external iPhone and iPod Touch battery with their Juice Pack line. They recently introduced their seventh generation product – the Juice Pack Air for iPhone 4. This battery/case combines protection for the iPhone 4 from real world azards along with supplying additional iPhone 4 usage time with the built in battery.

  Juice Pack Air for iPhone 4