On 2010-03-22, blueman wrote:

Could this explain why my battery died on a cold day after keeping the
radio on for about 30 minutes even though the car had just been driven
for about 45 minutes and even though the battery tested good under a
tester with a 100A load?

Yes. A soon-to-die battery with, say, one bad cell will take a charge
and run ok fer a days or even weeks. If you drive it daily and don't
start it too often, it will seem to be ok ....for awhile. As the cell
gets worse, so does the battery. The only true way to test a battery
is with a battery electrolyte tester, testing each cell's electrolyte.
That's why I will not buy a truly sealed battery. Many look like
they're sealed --no caps to remove to check electolyte or add
distilled water-- but the caps are usually under a strip of plastic
that can be removed with a little effort. If even one cell starts to
degrade, it's time to start looking for a new battery.

There are expensive electrolyte testers and there are inexpensive
one's. The cheap ones are usually small and have 4 plastic balls in
them. These are more than adequate. I've used them for years, even
when I was a professional mechanic. If all 4 balls float, yer good.
If even one ball sinks in one cell, that battery is not long for this
car-starting world.


Cars (and battery) are about 3-4 years old and never had such problems
in previous years.

Almost all car batteries in the USA are made by Exide. The more you
pay, the longer they last. Also, keeping one in good condition
--terminals clean, tight, charging system working, etc-- will also
increase the battery's longevity.

nb