A modern DVM has very high input impedance, which is another way of saying
it will measure a voltage even when there is almost no power behind it -- a
voltage that, in a sense, isn't really there. So what you were measuring is
essentially meaningless. If you want to demonstrate this, try putting a
large value resistor (say, 100,000 ohms) across the red and black posts of
your meter and doing the same tests -- you'll find that the batteries
measure exactly the same (there's a theoretical, unmeasurable difference),
but the strange readings won't happen.

BTW, at least down here in the warm climates (Boston), it is assumed that a
even a good lead acid battery will self discharge enough over the winter so
that it will freeze -- a trickle once in a while is good.


--
Jim Woodward
www.mvFintry.com


...
"Charles T. Low" wrote in message
...
I am taking the "bold" (for me) step of leaving my two batteries in the
boat
over the long, cold Canadian winter, a common practice, based on the
theory
that a good, well-charged battery won't freeze, and if it does, it wasn't
good and should have been replaced anyway. Furthermore, keeping it cold
should prevent it from self-discharging as quickly as it would in a warm
place.

So, I disconnected the negative leads (which sounds backwards, but that's
what many pros do), turned the switch OFF, and tested the voltages with a
digital multimeter. This was after an hour or so off the trickle charger,
which has been on for weeks. The water levels are fine.

One battery, my new-this-season deep cycle, read 13.45V. The older one,
the
starter battery, said 13.33V. These, of course are resting voltages, and I
realize not as valuable as voltage under load, and I didn't test the
sg's -
I may still do that. (Although my deep cycle batterry which failed
mid-season had had good sg's until it died, then they went way south in a
hurry.)

However, the thing which really puzzles me is that when (for some reason)
I
tested the voltage between the positive and negative posts of the opposite
batteries, i.e. neg on battery one and pos on battery two, and vice versa,
there was a momentary reading in the 5V range, which within a split second
dropped to 1.5V, and from there plummeted. I watched it down to about
0.6V,
but it was still dropping rapidly.

If I let them rest for a minute, the same sequence would repeat. So, I
disconnected the positive leads too, and wiped off any dust and grime from
the battery surfaces, but the same thing kept happening.

Any explanation? I doubt very much that it indicates any kind of a
problem.
But I'm not sure. Mainly, however, I'm curious and puzzled. Thanks in
advance.

Charles

====

Charles T. Low
- remove "UN"
www.boatdocking.com
www.ctlow.ca/Trojan26 - my boat

====