Unless you have a bad battery, that should not happen. But to prevent it from happening, put your car in Accessory mode if using your car radio to listen to the movie. And start your car once during the movie for a few minutes to charge the battery. If the rare case that your battery does die, go to the concession area and notify the staff. Almost all drive-ins have the equipment to jump start your car which they will do when the movie is over.