In article ,
J M Noeding wrote:

Keeping the battery charged is not the only reason to start the car once
a week.

Suppose it means that a car battery won't last long if you keep it
steady at top charge level, instead of decharge it down towards 50%,
sense the voltage level and charge it up to 14.4V (for this cold
area), and switch off the charger until it is down to 50% again....

As I understand it, that's exactly the opposite sort of regime that a
car battery prefers.

Car batteries are designed to provide large amounts of current for
engine cranking, even when cold. One of the tradeoffs in this design,
unfortunately, is that they do not tolerate deep (or even heavy)
discharge at all well. Discharging a car battery down to 50% and then
recharging it, repeatedly, is likely to greatly shorten its life. The
plates will quite literally fall apart.

Batteries having a different internal construction can handle deep
discharge quite a bit better. The older sort of "marine
deep-cycle" battery (designed for electric trolling motors) were
quite good - but I'm told that modern "marine deep-cycle" batteries
are more like car batteries in their design and no longer have a big
advantage in terms of deep-discharge life.

The best ones for deep discharge, today, seem to be the
starved-electrolyte (glass mat), and spiral-cell types. These are
often used for telecom backup applications, large UPS systems,
wheelchair motor, and electric-tractor/golfcart applications.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!