Mophie recently announced the 7th-generation of its iPhone battery boosting range - the Juice Pack Air - bringing battery life extension to the iPhone 4.

And Pocket-lint got its paws on one to give it the once over.

The device is described as "light-weight and ultra-thin" and we can't really argue with that. Although, it's a quite a bit bulkier than a traditional iPhone case, when you consider that it is packing a highly condensed lithium polymer 1500mAh battery, it really is quite petite. 

The Juice Pack Air clips onto your iPhone 4 like a regular case, although you do need to remove the top first to slide it into place. And that's because it's got a 30-pin Apple iDevice dock sitting at the bottom of it. It's this connection that draws the power from its battery into the iPhone.

After charging the device for a few hours (it takes around 3-4 hours for a full charge) via the supplied USB lead, the LED battery status indicator will let you know how much power it's packing and it can then charge your iPhone's battery on the go.

The official guidelines state that, with a full tank in the Juice Pack Air, you'll get an additional 6 hours of 3G talk-time (12 on 2G), 36 hours extra music playback and 9 hours of video playback.

iPhone users will know, however, that when you throw in some browsing and downloading, the battery life takes a serious plunge. A good way to judge the Juice Pack Air is how much of a boost the device gives the iPhone battery. We charged it from empty to 70 per cent with a full Juice Pack Air battery and from 17 per cent to 90 per cent as well, So you can expect around a 70 - 75 per cent battery boost.

The Juice Pack Air has a standby button, so as it isn't always charging - you just boost your battery when you want to, and the case has all the necessary holes so as you can access all of your iPhone 4's slots and buttons. The back has a nice soft-touch, rubberised finish and the sides are a sexy metallic silver.

The Mophie Juice Pack Air is available now and will cost you around £70. It's a handy tool to have lying in your bag (if you remember to charge it that is) and for some people, it could even act as a permanent iPhone 4 case as it really doesn't add too much bulk to the handset.