anybody know if its damaging to your zune/ipod to leave it playing on the charging dock all night long, every night?

i like having my zune playing at night while i sleep but my dock doesn't have a sleep feature or anything, so if i leave it on, it stays on all night, and i didn't know if this was harmful to the battery life.

Will it affect battery life? Maybe.

I've had my iPod plugged in my car for the past 2 years. (Literally) And I haven't noticed any differences. I hardly take it off the charger and listen out of my car though.