Q: I have a third-generation iPod and have recently purchased a new 160 GB iPod classic. Can I charge the battery on the new classic using the third-generation charger and dock?
A: The short answer is yes.
All charging accessories for any Dock Connector based iPod are compatible with later generation iPod models. Although the new iPod models do not sync via FireWire (which was the method used by the third-generation iPod), charging via FireWire remains supported.
The only exception to this would have been charging a third-generation iPod with some of the newer accessories, which use USB-based charging. The third-generation iPod only charged using FireWire, and therefore does not support many of the newer charging accessories.