The nominal range for automotive systems is 10-16v. If you are designing anything for automotive use that doesn’t work reliably in that range, you are manufacturing problems for people.

This. Most cars nowadays come with the so-called "smart" alternators that vary voltage wildly depending on the current driving conditions.

One minute you might be accelerating and the onboard voltage drops as the battery supplies most of electricity. Then, as you reach the crest of a hill and start engine-braking, the car frantically tries to convert all the available kinetic energy to electricity, raising the onboard voltage to quickly charge the battery.