New stuff won't charge due to the voltage differences (I just experienced this going from 1st ten nano to an iTouch), but you can get one of these to make it charge for you whenever the car is on:
http://www.amazon.com/Scosche-passPORT-Charging-Adapter-iPhone/dp/B001HN6CVA
Here's the update. I received the 4th generation 8GB iPod nano. It plays with though my car stereo by itself but does not charge so after couple of days it begs for juice. The Scosche passPORT adapter is nearly the same size as the nano. It allows the device to charge.
My songs are encoded with a pretty high bit rate so the nano holds about 1450 songs (half my library). That's much more than the 1GB nano offered so I am rediscovering music I didn't know I had.
The one downside is that the new iPod nano shuts off overnight. The old one would fire up when the car started. Now I must physically press the power button on the new nano.
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