My iPod car adapter has great sound but won’t charge the iPhone 3G or any of the new nanos. The same problem also affects my Bose Sounddock. After a little research, it seems Apple removed the firewire-based charging capability from their latest products, and many older accessories that charge via the dock connector emulate a firewire connection. The passPORT from Scosche is a little box that has a female dock adapter on one side and a male on the other; it simply converts the firewire power into the pin and voltage configuration used by USB, which is supported by the newest Apple gear.
Link: iPod won't charge in your car?