Saw this in poundland today. Basically you put 4 AAA batteries in it which obviously you can get from poundland as well
12 Kodak or 8 Panasonic or 2 Rechargeable
And it has a lead with a Female USB connector on the end so you can plug your USB phone/mp3 usb lead cable it to top up the battery.
Thought this might be good for emergencies.