The LithiumCard Pro is the follow-up to the original LithiumCard – a credit card-sized external battery for the iPhone and Android.
This model is just as slim as the original, but packs three times the capacity and more power. It boasts a 3,000mAh charge – that's enough to fully charge the new HTC One M9 or iPhone 6. There's also 3A of power, which means it should charge three times quicker than a standard Apple wall charger.
Of course we can't verify these claims without testing it for ourselves. But if true, that's mighty impressive for a device of this size.
The makers claim you'll get 1 per cent of charge for every minute you leave your phone plugged in. Again, impressive.
The device charges using its full-size USB cable, and is available with microUSB or Apple Lightning cables to power up Android, Windows or iOS devices. When not in use, the cables fold into the body to be out of the way.
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It also has another USB port, dubbed the HyperPort. This lets you power up another device at the same time, so you can juice up your iPhone and Apple Watch simultaneously. Or your Android phone and Android Wear watch.