Just FYI, over 15volts will ruin your 12volt battery, literally "cooks" it
Battery's sole, and only, purpose in a car/truck is to start the engine
After startup all electric power comes from alternator, at minimum 13.5volts
A car/truck battery will be 12.8v to 13volt when brand new
12.5volt after 3 years or so
12.3v after 5 to 6 years and time to shop for battery sales
12.2v and lower is a "dead" battery, just hasn't stranded you yet
Alternators work based on "push back" in the electrical circuits in the vehicle
Push back is what happens when you turn on a 50watt(4amp) light bulb
The bulb sucks in the 50watts of electricity when turned on but the once its on it "pushes back" to just stay using 50watts(4amps) of power
Engine is running and Alternator is on, and lets say vehicle needs 40amps of electricity, alternator cranks out amps until it gets push back, at 40amps and then stays at 40amp output, that's what voltage regulator does reads push back
If you turn on driving lights, 10amps, push back DROPS and voltage regulator adds more amps until it gets push back again and its now outputting 50amps
Now when you start the engine the battery gets drained, takes 60-75amps to crank an engine, so battery has a lower push back, it needs amps to recharge
So just after startup you might see voltage from the alternator at 14.8volts, but ONLY for a few minutes until battery has been recharged
Then the battery starts to push back and voltage regulator drops amp output down to only what vehicle electrical system requires, so should be under 14volts, 13.8v to 14.2v depending on year and how many amps it needs
If battery is failing or voltage regulator is then voltage above 14.8v may be seen even after a 10 min drive, this is bad for a good battery and bad for the vehicles electrical systems as well