How long will I be able to listen?

I am planning on going to the drive-in this weekend with my Cruze. This drive in has a radio station dedicated for the movie so I plan on using my radio for the audio. I also would like to have the AC going a little bit so it doesn't get stuffy. I would just have the windows down but here in MN not smart to do unless you like getting eaten alive by mosquitoes.

So my question is how long will my battery last with both the radio and AC on? Will I be planning on starting the car to keep that battery charged?
In case it makes a difference, I have the Premiere audio with Pioneer..

Thanks