The good ol' Drive-in double feature evenin'

Back in the 80's we used to go watch movies at the Drive In (Saw Robocop when I was like 7 years old on the backseat of a 79 T-Bird)

One thing I wanna do is go back to that drive-in (still opened !) with my 74 Dart Sport.

But I worry about Battery life... I've heard horror stories about new cars unable to keep enough charge after a double feature to start the engine when it's time to go.

I was wondering if the Dart has an accessory position on the ignition switch and if you guys had that kind of experience with your a-body (i.e. newer radio like the RetroSound Redondo RS, watchin' movies for like 4 hours before starting the car, etc.) to share.

(Edit: I don't have the car on hand right now it's being worked on at my local performance shop)