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Here is another iPhone 4 cover called mophie juice pack for iphone 4 made by Mophie. This iPhone 4 cover can also be called mophie juice pack external battery case because it doubles the battery life of iPhone 4. Mophie has already developed iPhone cover which until now has extended battery life of iPhone 3G , iPhone 3GS and iPod Touch. Mophie juice pack for iphone 4 cover price is expected to be $ 79