will Sansa be hurt if I play it while charging

MP3 players Sansa Fuze
1

Hello!!

I play my Fuze v1 in my car  using a FM Transmitter that also charges the Fuze.  I use it all the time and as a result the Fuze is almost always charged.  Am I damaging or shortening the life of the battery by doing this.  Would it be better to use a FM Transmitter that does not charge the Fuze. 

Thanks