AA Rechargeable Batteries
This NiMH AA cell can be used in normal battery applications and can be recharged simply by plugging into a USB port.
They have a capacity of 1300mAH, which is not great considering you get 2500mAH batteries. Also they take 5 hours to charge (that is very poor), the 2500mAH batteries can be charged within an hour if you have the right sort of charger. (UNiROSS Sprint 1H).
I would still buy them, just for the hell of it, to think you can plug them into any USB socket, such a laptop, PC or XBOX 360, so while you are gaming, your batteries for your wireless controller are charging. This is a genius idea if there ever was one. I believe they cost £12 for two.