Date: Thu, 14 Mar 2002 23:45:34 -0600
Reply-To: Joel Walker <jwalker17@EARTHLINK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Joel Walker <jwalker17@EARTHLINK.NET>
Organization: not likely
Subject: FYI: Battery Life
Content-Type: text/plain; charset="iso-8859-1"
from the April 2002 issue of Road & Track
(names of the automobiles have been changed to protect the innocent).
;)
Question to Technical Correspondence, edited by Tom Wilson:
Battery Life
What determines battery life? I own a '91 * with over 250,000 miles on
it and the original battery still seems strong. Obviously i do a lot
of highway driving but even when I have been away for three or four
weeks, upon my return the car fires right up.
I also have a vacation trailer with an expensive heavy-duty deep-cycle
battery, but it seems to last only three or four years at most. My
small * battery is such a surprise to me that I am now afraid to even
look at it in case I jinx it and it dies. What would make one battery
last so much longer than another??
Reader in Hope, BC, Canada.
Answer from R&T:
Well, congratulations on a decade of service from an automotive
battery! Your experience far outstrips the normal three-to-four year
battery life span.
There is no single factor in determining battery life, although
battery manufacturers say three years is normal, five years is
exceptionally good and eight to 18 months is a sign that something is
wrong. It seems these figures hold true for any quality battery, no
matter what the warranty says. Many battery warranties are 100 percent
up to three years, then prorated from there, which ought to tell us
something.
Anyway, from a design and manufacturing perspective the number and
thickness of the plates, the amount of space available for the
electrolyte between the plates, the acidity of the electrolyte and
certainly the use of either antimony or calcium in the lead alloy
affect battery longevity. Of these, the advent of calcium-based grids
for premium maintenance-free batteries in the mid-1970s has been the
greatest boon to long-lived batteries. This is because calcium
batteries don't gas as much as antimony-based units, helping to
maintain a more constant electrolyte pH and keeping the plates covered
in liquid. Excessive acidity or dried plates from gassing hastens
plate failure.
Smaller batteries with high cold-cranking amps capacity are also not
endurance hall of fame candidates, especially in hot climates. Such
batteries rely on large surface areas from numerous, thin plates to
have a ready supply of active material on hand. This increases
cranking capacity, but the thin plates succumb more quickly from
electrolyte corrosion.
Your deep-cycle RV battery should last longer than the typical
automotive battery because it trades many thin plates for relatively
fewer, thicker plates that better withstand deep discharges. To make
up for their lack of electrical punch, such batteries are typically
larger to accomodate more of their bulky plates.
While likely not a factor in your *'s supernatural life span, plate
separator design can still play a part in the short life spans of less
expensive batteries. The bargain specials might use a cellulose-based
plate separator fitted directly between the plates. These so-called
leaf separators corrode away, consigning that battery to the recycle
heap. Most modern auto batteries use superior envelope separators,
which hold the plates via pockets molded into the case.
Then there are environmental factors. Batteries prefer an even state
of charge, minimal gassing, and cool electrolyte temperatures if they
are to make it four years. An overeager charging system or simply hot
southern summer temperatures boil away the electrolyte --- there's our
gassing problem again --- while a weak charging system can lead to a
big discharge. Interestingly, because overcharging most quickly kills
batteries, typically alternators are regulated to provide relatively
low charging rates. This may mean a chronically undercharged battery
following a jump start after the headlights were left on overnight.
The jump gets the car going, and the alternator can charge the battery
back to usefulness, but often not to a truly full charge. Shortened
battery life follows due to sulfation and crystallization when
undercharged. This is a typical problem with deep-cycle batteries
because of their duty cycles, but is a battery killer whenever
undercharging is found. Interstate says battery deterioration is rapid
whenever the battery is below 75 percent state of charge (12.45 volts
on a digital meter or electrolyte specific gravity of 1.225), and that
batteries should be kept at 100-percent charge at all times for
maximum life.
Corroded terminals and cable ends aid electrical leakage and hinder
charging, also leading to chronically "low" batteries. Obviously this
is a major contributor to short battery life.
Naturally, plain old use wears out a battery. The more a battery is
cycled, the more active material is loosened and sheds off the
positive plate. Nearly all is restored by charging, but not 100
percent, and so after five to six years, there is little left to give
on the positive grid and the battery dies. However, at the same time
negative material is shrinking away from its grid and so the typical
three-to-four year life span. It's the negative material falling off
its plates that causes the more gradual decline in cranking power, by
the way. It's why an older battery can work the lights and radio,
soldier on through summer, only to fall dead the first cold day of
winter.
So, while the variables are seemingly endless, we'll say your driving
cycle is probably optimum for your battery and charging system. In
other words, your standard drive is long enough to fully recharge the
battery after the drain of starting the engine, but not too long to
pose a threat of overcharging. Don't underestimate your cool British
Columbia climate, either. We consulted both Douglas and Interstate
Battery, and both were adamant that no matter what, put your * in
Phoenix and your battery would never have made it half as long. So,
with a minium of hot days, attention to battery terminal cleanliness,
a well-regulated charging system, and a maintenance-free battery, you
have proven 10 years' worth of battery life is not impossible. If only
the rest of us could come close!
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