Handy case to extend the battery life of your iphone currently on sale at o2 due to 20% off accessories. There are a few sellers on amazon who are around the same price but you might feel safer getting it from o2 direct.
Also available instore if you have the o2 priority moments.
(the code is 200001001779178 if you dont have o2 :)
White version - http://shop.o2.co.uk/accessory/Juice_Pack_Air_-_White
Power your iPhone on the go
Rechargeable external battery
Slim design and lightweight
Virtually doubles your battery life