This Nyko iBoost Battery Pack for 4G iPods is suitable for 20GB and 40GB iPods, and their Docks. It has been reduced from £40 to just £9.99 delivered at Play.com (cheapest elsewhere is £37!).
Specifications: Ultra-Slim Rechargeable Battery Pack for iPod. Up to 16 hours extra play time. High quality lithium-ion battery cells. Charge both the iBoost and the iPod, and transfer files, all at the same time. Fits 20GB and 40GB iPods, and their Docks. Charges via AC adaptor supplied with iPod or via computer's USB or FireWire port. Can be charged with car charger (not included).Slim and compact in matching iPod white