The newest Intel® NUC Kit 5CPYH supports power adapters of 12 and 19 V. It requires power supplies with output of 3.0 A minimum.
Your current NUC might work with your car specifications.
The Technical Product Specification of Intel® NUC Board NUC5PPYH is the following.
During engine cranking the starter motor will draw a great deal of power. Causing the voltage to drop well below 12 volts during this time.
Yes, and brownouts like this can possibly do damage. It's best to have a regulator that guarantees voltage (or shuts off completely if it can't) and eliminates spikes...
Also most vehicle DC power is pretty dirty and fluctuates quite a lot. If I was going to use one in an automotive application think I like to have some sort of isolation, voltage regulation, and filtering rather than connecting it directly to the vehicle power. You might get away with it, but probably going to shorten it's life. it's a pretty expensive piece of equipment to do that too. I wouldn't do it.
I heartily agree!