The Juice Pack air simply slides over your iPhone 4/4S and provides a Micro USB connection for external charging. While some dislike this because it means you need to get another charger to carry around with you, I actually like it. It means that you now have double the potential to charge your phone whenever you see a charger: the odds are that if you can’t find an Apple dock connector, you’ll be able to find the industry standard Micro-USB plug.
The Mophie Juice Pack Air is relatively slim and includes cutouts for the power buttons and headphone jack. The hole for the headphone jack is quite generous, bit some may have issues with headphones that use a large plug since it is not flush against the iPhone.
A series of 4 LED’s on the bottom of the case allows you to check the battery level of the case separately from your phone. A small rocker switch to the left side of the case in this image selects if you’d like the phone to be charging from the case, or used purely as reserve.
The top 1/3 of the case is removable to allow access to your phone, occasionally when removing it from your pocket this could become lost or detached from the rest of the product. While this sucks, at least it isn’t like previous generations of the Mophie cases where the bottom detached, leaving your phone without additional charge if lost.
I’ve found that the Mophie Juice Pack Air will recharge your phone from dead about once, allowing a heavy-user to go nearly a day and a half without recharging. Those that are light-users could go upwards of two days.