Using code ASTROE4B, you knock £10 off the price of this Anker Astro E4 13,000mAh portable charger, bringing it down from £29.99 to £19.99.
Claims to charge the Samsung Galaxy S4, for example, "more than 3 times".
Adapter required for iDevices (iPhone, iPad, iPod touch).
Delivery is £3.99 (total £23.98).
(Thanks to rapuchy at HUKD)