Griffin, maker of various Apple accessories, has confirmed that its PowerBlock Reserve product is finally coming to Britain, more than a year after it appeared in the USA.

The device acts as both a USB wall charger and a reserve battery for the iPhone and iPod. The battery is magnetically attached to the charger unit and can be taken away with you to add a little more juice to your portable device in emergency situations. There's an LED indicator that tells you how much battery remains.

Griffin doesn't specify exactly how much extra battery life you'll get with a full charge from one of these devices. Be aware, too, that the battery hangs off the bottom of the device, which actually blocks the headphone socket on the iPod Nano and iPod Touch. As a result, you won't be able to listen to music while charging.

The device will be available from Apple stores in February, costing £30.