I recently added an iPod interface to my Accord: http://www.amazon.com/gp/product/B001JT5G4G/ref=oh_o02_s00_i00_details
It has two connections: the regular Apple 30-pin iPod dock cable which plays back and charges and then an AUX 3.5 mm headphone connector.
I get the best sound when connected to the Apple connector, but it is also charging it at the same time. I really don't use it much outside of my commute to work ~1 hr. per day, so is it bad for the battery to be plugged in all the time? The car interface won't overcharge it; it stops when full. I just didn't know if I needed to actually use the Li-ion battery in the iPod to keep it useful when I do need to take it unplugged.