Am I incorrect in my thought process here?
Since a lot of the electricity produced by the alternators in cars is never used because the battery is fully charged, running additional electrical devices doesn’t actually cause your vehicle to consume additional gas. In this fashion, day-time running lights and/or driving with your headlights on doesn’t actually cause you to consume more gas.
This site seems to think it does.
Update: Nope. It seems my thought process was incorrect. This page lays it out very clearly.