Rechargeable Batteries for Magic Trackpad

I've just bought a Magic Trackpad and Wireless Keyboard with my Mac Mini and wanted to know what you guys thought the best rechargeable batteries for them are, given that they are going to run out eventually. Its only been a week and my trackpad is down 10%.

EDIT: Well thank you all, seems like I should buy the Eneloops. Are they available in UK stores, or should I hit Amazon?