Jim Weir wrote:

So why was there 12 volts to begin with? Because Detroit started making cars
with a much higher compression ratio and to turn the starters over, the old 6
volt batteries weren't cutting it. Bingo. Two 6 volters in series gives 12
volts and that was close enough for Detroit gummint work.

Actually the auto industry is moving to a 42 volt system in the future to handle
increasing electrical requirements, plus more accessories (e.g. oil pump) may be
electric in the future. Where can you find more information on this? Why
http://www.42volt.org of course.