Battery packs for iPhones often dramatically extend the useful lifetime of Apple's devices, but they also add considerable bulk and rarely feel like natural extensions of the iPhone itself. Mophie wants to change this with the Juice Pack Air; we'll see not only whether it accomplishes its intended goals but whether it or the original Juice Pack is the better choice.

design and hand feel

The core battery section of the Juice Pack Air is, from a basic perspective, very familiar to anyone who's used the regular Juice Pack for the iPhone 3G. It almost entirely envelops the bottom two thirds of the phone, excepting the screen. A pair of scooped-out sections near where the iPhone's Dock Connector plugs in ensure that calls and audio aren't muffled by the case; we didn't have any problems with audio in testing.

As the MacBook Air-inspired name suggests, it's decidedly thinner than the earlier model. Where the original at least doubles the iPhone's effective thickness in your pocket, the Juice Pack Air only extends that by just over half of the iPhone's original thickness. In the pocket, it's noticeable -- though we'd say it's still comparatively thick. This isn't for owners with tight pockets.

Almost more significant than the thickness, though, is the top shell. The Air adds a second piece that offers very nearly complete protection of the rest of the iPhone's back; the only exposed areas are those needed for the buttons, camera lens and headphone port. It's a very welcome addition and may be worth the sacrifice for those truly worried about scratching or dropping the iPhone the wrong way. Pressing the buttons is made slightly more difficult, but not so much as to be inconvenient. The only true complaint is that it's particularly difficult to remove once it's attached, but it's thankfully optional.

Other features are again very much familiar, but with an important twist. You still have a USB port to sync with a computer while charging the case, and a four-light, button-activated battery gauge. However, it now uses what appears to be micro USB instead of mini USB and is therefore more dependent on keeping the proprietary cable. Thankfully, there's now also a switch to toggle whether power flows from the pack to the iPhone. It's an extremely handy option to prevent the Air from recharging the handset when you don't need it -- such as when you're about to return home to a charger -- or simply to run on the iPhone's own battery first. It's not a factor very often but is appreciated.

One key change from the standard Juice Pack is decidedly worse, though: the texture. The full-size model has a rubberized grip that renders it much easier to hold, but the Juice Pack Air has a glossy, smooth plastic finish much like the iPhone 3G itself. Grip as a consequence is no easier. Outside of it fitting more snugly in the hand due to girth, the Air still triggers worries that it might slip out of your hand in too-casual handling. We'd be willing to pay extra just for the better surface, and the full Juice Pack's extra battery capacity makes that leap all the more tempting.

by Jon Fingas