Mophie has launched the new Juice Pack Air, an Apple-certified external battery for the iPhone 3G, which also doubles up as a protective case.

The Juice Pack Air is the world's thinnest "certified" external battery for iPhone 3G, and will provide you with virtually twice the battery life of the iPhone alone, all in the full protection of a hard-shell case.

The case features a rechargeable 1200mAh lithium polymer battery, but the nice touch is that it doesn't have to be on all the time. The "standby mode" will allow you to conserve the power of the battery and simply use the Juice Pack Air as a protective case.

The integrated 4-LED charge status indicator will allow you to check how much power is left in the battery. When you need to recharge it, pass-through USB charging will allow you to power the battery while simultaneously linking up to iTunes as well.

The Juice Pack Air will be available this spring in a choice of black, white or purple from Apple stores worldwide, and online from Mophie's website. American prices have been announced at $79.95, with European prices to be confirmed.