On New cars like a 08 vue, does the alternator stop charging while driving once the battery is fully change to capacity? I've read that some systems do. For example, start up the car and the output is 14.5v to the battery. But once you drive it for several minutes, the regulator or ecm will tell the alternator to drop the voltage to 12.7. Is this true? I'm wondering because mines does exactly this. Matches to the tee. I recently changed my battery and or of curiosity I put a volt meter and watched the voltage as I drive. And that's the pattern I see.

 

The initial 14.5 volts are to build the back battery up to full charge.


Once the battery is fully charged the electrical system runs off the alternator with the battery acting like a capacitor. If you do not know what a capacitor is then; It is an amperage storage device which is used when high draw items like say AC is initially turned on. The alternator does not have the capability to store amperage like a battery or capacitor do.


A perfect example is when you in your home have 120 volts running your air conditioning unit outside the house. If the unit did not have a capacitor the unassisted 120 volts could not handle that initial fan motor and compressor load which is put on the electrical system when the unit comes on. Damage to both the fan motor and compressor would result or you would constantly blow breakers. Use a Capacitor and that issue is non-existent.


I hope that this helps you understand how charging systems and electrical systems like you mentioned function.