mm writes:

On Mon, 22 Mar 2010 08:59:21 -0400, 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?

And just yesterday (which was in the high 40's) my other car ran down
the battery while cleaning it for about an hour with just the radio and
door lights on?

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

Maybe the battery is good but the charging voltage is low. Have you
measured it. Should be about 14.5 iirc. If too low, it won't put
enough into the battery, even a good one.

Well my tester also measures charging voltage and it seemed ok...


Maybe the charging voltage is low because the fan belt is loose that
powers the alternator. Or maybe their is tension thing for a
serpentine belt and the spring is getting weak.

How do these ideas sound to you guys? Because I'm having the same
problem described above, and I have to try to fix it soon.

Interestingly, I took one of the cars into Advanced Auto Parts today and
they had some "fancy" (proprietary they claimed) computerized battery
tester that supposedly does all types of things that a standard 100A
load doesn't test. And that battery tested just fine - it measured a
voltage of 12.79v and a CCA of 574 (vs. rated 582). I was surprised
because I was almost sure that they would have "rigged" the test to sell
more batteries so that just about any 4 year old battery would test
bad. But the guy was nice, helpful, and surprisingly honest....

While the screen and printout were pretty cool, not sure I believe it
does all that more. Also, not clear to me how you can measure CCA at all
accurately when the ambient temperature is not 0F but I assume it does
some type of temperature adjustment since the screen and printout had a
temperature measurement on it (though since it said 73F, it seemed like
maybe it was the room temperature of 73F where the machine was stored
and not the outside temperature which was in the low 40s - though maybe
there was a temperature probe in the battery connection and that was the
under the hood temperature).

But in any case, if the store selling batteries tells me my battery is
good, it seems like it probably is.