mike wrote:

Car generators have had regulators for as long as I can
remember. 1955 was the oldest car I've had. Was sloppy.
Just a relay that had a soft spring that gave a couple
of levels of control.

So I take it then, it was just designed to
destroy the battery ? :-) That sounds like the
car companies I know and love.

Does it ever stop charging the battery, or does
the '55 battery get ruined ? There are two ways
to ruin a battery - sulfation (too little charging
between uses) and corrosion (too much charging).

https://en.wikipedia.org/wiki/Lead%E..._desulfatio n

I had the exact opposite problem here with my car,
where the alternator and voltage regulator were
hardly pumping any current into the battery. And
I couldn't really tell if the net charging rate
was sufficient to keep the car starting or not.
I kept having to throw the charger on it in the
winter. And the headlights behaved normally, not
like headlights behave on older cars (dim at low
RPM). It was almost like the voltage regulator
wasn't regulating to the correct voltage.

Every time I work on cars and their charging systems,
none of my measurements make any sense :-) The car
battery voltage is never even remotely close to
textbook, and I end up not really knowing what's
going on. I have a hydrometer, and that's the only
sanity check that really works.

https://en.wikipedia.org/wiki/Hydrometer

Battery hydrometer

... Tables are used to correct the reading
to the standard temperature

Paul