how long can I play the car radio before it drains the battery?

[dpopiz]

if I just play it at a fairly low volume, how long will an average old battery last?

 

[FleshLight]

Well since most batteries die if you forget to turn off the headlights, I'd say 72 hours.

 

[KLin]

why don't you time it and let us know?

 

[Pepsi90919]

some newer cars (GMs) have automatic battery run down protection

 

[KingNothing]

One time I ran my friend's 300watt shelf system off my car battery using a power inverter for 2.5 hours, and my car still started so...probably longer than that depending on how much current your audio system draws.