Mophie has announced the 7th-generation of its iPhone battery boosting range - the Juice Pack Air - which it says will "virtually double" your iPhone 4's battery life.

The device, which is "light-weight and ultra-thin", clips onto your iPhone 4 like a regular case, but boosts your battery on the go. Its soft-touch casing will also protect your iPhone 4 from any bumps and scrapes.

With 3G on, you should get an extra 6 hours with the Juice Pack Air's highly condensed lithium polymer 1500mAh battery, and double this if you're happy to go 2G only. You should get 36 hours more music playback, and 9 hours extra video.

The case also works as a sound enhancer, with sound being redirected to the front of the device due to its shape.

There's an LED light display to tell you how much power you've got left in its tank, and you don't need to remove it to charge or sync your iPhone 4.

The Mophie Juice Pack Air is available now and will cost you around £70.