We had the opportunity to review the Mophie Juice Pack Air for the iPhone 3GS back in 2009. The model we will be looking at today is the Juice Pack Plus, but they also offer a slightly cheaper Air version. The difference being the Plus model has a 2000 mAh battery capacity vs. the 1500 mAh of the Juice Pack Air. The Juice Pack Air for the iPhone 3GS sported a 1200 mAh batter capacity. This additional capacity does increase the overall size slightly, though it seems to be fairly minimal.