On Saturday, June 22, 2019 at 6:00:41 AM UTC-4, Brian Gaff wrote:
Yes indeed, the nominal output of an alternator can be as high as 15 volts,
but even a fully charged car battery is only 13.8v as far as I know and
these days, I'm sure the direction of current flow and voltages are
monitored very well by the computers. In the old days it was a bit of a
black art just relying on the ability of the alternator or dynamo in the old
bangers.

Nonsense. Cars used voltage regulators for better part of a century and
they are simple electronics which is well understood. And, AFAIK,
that is STILL how it's done, all the FUD here notwithstanding. Some
cars may have something more elaborate, but it's obviously not required
to keep the battery correctly charged, which was the OPs question about
charging.