Accordign to my gauge, the average regulated output is 13.5V. When I first turn the car on, it will show a full 14.4V during warm-up, but during normal operation, voltage stays between 13.5 and 13.9 volts.

 

The charging system will not maintain that voltage under load. The alternator needs to charge at a higher voltage to charge the 12.5V battery. For electrons to flow, there needs to be a difference in potential.
The 14.4V number does not exsist in a car, but it is the new industry standard.