Reduced to clear, down to £5 in Robert Dyas instore (Didcot branch in this case). No more left in the store there on the shop floor I'm afraid, might be worth calling ahead to any branch unless you're passing. They were on the display with all of the batteries and the Robert Dyas product number is 154663.
It's a portable USB charger that claims to give up to 3hrs to your smartphone in extra talk time.
Currently £14.08 on Amazon - http://www.amazon.co.uk/Duracell-Mobile-Phone-Portable-Charger-Black/dp/B005EF2TG4