This very much depends on the car.

Most modern computer controlled cars will not discharge the battery at idle unless you have a powerful sound system or an alternator that’s already on its way out. And they can adjust idle anyway if needed, most will increase idle when AC is turned on now to compensate the increased load on the engine. Driving the AC compressor is such a light load compared to the moving a 2 ton vehicle.

Also, many newer cars may even run an electric compressor instead of one driven off the motor. Think hybrid vehicles, it wouldn’t be feasible to have an AC system that turns off half the time if it’s running on the electric motors.

What you might deal with is heat soak if the fans can’t move enough air over the condenser core. But modern vehicles are immensely more efficient than even 10 year old vehicles.

Id still be using my clamshell iBook if it worked and supported a modern-ish browser.

My eeePC only got sidelined because 4gb of ram is now too little for kubuntu releases. (I was going to install Debian, but after 30 min on it’s SLOW SSD it failed and I haven’t tried again) And I had issues with the screen resolution being too low for the smallest settings window before.