What should alt. volt's show under normal condition's. Mine shows 13.3v-13.5v most of the time going at road speed's. Stay's about 13v-13.1v with A/C on fan on high. When not in use I keep a battery tender hooked up to it.

 

The range of the numbers sounds OK but the number itself is about a volt or so low. That is easily accounted for by a possible inaccuracy in the car's voltmeter. If it starts OK without issues electrically it's probably just fine. You could find an accurate voltmeter and compare the readings to make sure your car is fine.
Ron

 

My voltage readout averages about 14.1.