Do car engines idle higher when the battery needs charging?

If alternators needs higher engine speed to output more power to the battery then is the engine supposed to idle higher when the battery is lower? My dad said that the only reason the engine idles higher when I start up the car is to warm up and that it has nothing to do with the alternator or battery. The car I drive is a 1989 honda accord. What do you think would happen if the car engine is already warmed up but the battery voltage is low?

You sound like you want to learn about cars and how they work which is great! Motorhead answered your question but I want you to check this video out and try playing around with a multi-meter yourself. Maybe you can try reving the engine and seeing if the voltage increases and if not, try to figure out why. Plus this video will give you a lot of good information!

You dad is right.
It would be nice if they did make the engine rev more if the current was needed, but no one has implemented that yet except on hybrid cars.
But they do have it wired so that it will rev more if the engine is cold, you turn on the AC, or something like that.

The load from the alternator is not sufficient to require an increase in engine RPM to charge at its maximum capacity. The load from A/C is more significant, and often turning on A/C also raises the idle RPMs. We might quietly note cars will pass emissions tests more easily with A/C turned on to increase the RPMs.