If you’ve gone from the iPhone 3GS or iPhone 3G to the iPhone 4, you’ll know that the battery has been vastly improved, however you’ll also know that the battery is still unlikely to get you through a whole day and to the next with moderate to heavy use.

Hoping to allow you to have your cake and eat it, Exogear has followed company’s like Mophie and Mili in creating a “slim line” battery case for the Apple phone that lets you keep on making calls and surfing the web that little bit longer.

The Exolife iPhone battery case, £59.99, is a protective exoskeleton for the iPhone 4, iPhone 3G and 3GS, which is fitted with a rechargeable external battery to give your iPhone the extra power that you need.

It will, of course, increase the size of your phone both in thickness and in length (about 10mm).

Doubling the battery life of your iPhone (Pocket-lint's tried it and it works) there are a range of different case colours available aside from the “smoke” coloured one that you get in the box - green anyone.

As with other battery cases it won’t work with any docking station or speakers as the new case turns the Apple 30-pin connector at the bottom of the phone into a USB one instead. You will, however, still be able to charge it via USB and sync it with your computer with the included cable.

You’ll also be able to turn the battery element of the case on or off so you don’t have to charge it from the start, but only when you need it.