A little research is a wonderful thing. Nigel Calder has several relevant
tables -- Boatowner's Mechanical and Electrical Manual, second edition,
International Marine, 1996, page 39 (Calder was by far the single most often
seen book on voyaging boats on our circumnav.)

At 10C, a battery will self discharge about 5% per month (I'm interpolating,
but that's probably a good number). So, if you start fully charged, after
five months, you'll be around 75% charged and have a freezing point
around -40 (C or F). That's probably safe, as Charles says, particularly in
an.area where 10C may be a hot day. This may even be one of those strange
situations where something is less likely to freeze in a really cold climate
than in a more temperate one.

I suspect the standard practice here may relate to several things:
a) the temperature during storage is often above 10C
b) the storage season may be as long as 8 or 9 months, particularly in Maine
c) the battery may not be fully charged to begin with -- many marine
batteries are never fully charges
d) general conservatism


--
Jim Woodward
www.mvFintry.com


..
"Charles T. Low" wrote in message
...
Thanks again, David,

These batteries are enlosed in wood. Fingers not touching probes. It's the
cheaper meter. I won't worry.

Now, to answer other messages all in this one: Butch (JDavis1277) says
that
freezing is bad. Yes it is. But a charged battery will not freeze. We
leave
our cars outside, and it gets down to minus 30 C here some nights in
Jan/Feb. (Burr.) People who store "summer" cars in their unheated garages
often leave the batteries in, and never give them a second thought until
Spring. Lots of boaters leave their batteries in. If there have been
problems at your marina, are they due to poorly maintained and
incompletely
charged batteries being left in the cold? Is this reasonably avoidable by
good maintenance and monitoring?

Jim Woodward says "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." It's
good to err on the side of caution, but if the battery is clean (to avoid
trace currents between the posts), the electrolyte good, the charge high,
and the plates in good condition (but how would you know?), then a battery
will last longer in the cold that in the warm. I know knowledgeabe boaters
with batteries over ten years old that they leave in the boat over the
winter, with never any trouble. Maybe they're just lucky. I used to keep
mine in the basement, then moved them to my unheated garage, and put them
back on the charger for a few days mid-winter - but they never needed it.

Paul Schilter says "If you put a small load across the battery such as a
small light, you'll get a more realistic reading." I'm going to do more
research into this. Some dockside "authorities" recommend a big load, like
monitoring the voltage while starting the engine. Is a small load really
enough?

Thanks to all.

Charles

====

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

====

"David Ditch" wrote in message
...
Are your fingers touching the probes?
Is it a good $200 meter or a cheaper $40 meter.

Unless you can see leakage I'd not worry about it.
If your battery tray is metal like a car and it measures differently
when
you remove the battery from the tray, then you may have a leak
somewhere.

David