Your batteries would probably last longer if you fully cycled them at least once a month.
Top charging even LiIon batteries will reduce their lifespan over time. I'm pretty bullish about not charging up my devices until they run dead, but it does keep them running for a long time. How long? I always end up replacing the device before I have to buy a new battery.
I have four iPods and the only one that holds a weak charge was the one that I used to use in my car (top charged through the adapter every time I drove somewhere).







