I use my trickle charger every month due to the shorter commutes in traffic preventing a good charge.
Also use it on the 2nd weekend car that sees less mileage.
Lastly, I use it the day before I go to a drive-in theater to ensure my batteries are good for the full movie.
The car stereo actually sounds pretty good, even with the movie in FM stereo broadcast only. Cuz of the enclosed car environment.