[A4] Dead Battery

[Sean Reifschneider]

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On 02/02/2010 07:21 AM, Richard Hurt wrote:
> Wow, my battery died like I've never seen it before.

This sounds similar, though definitely worse, than what happened with our
'97 A42.8q when it's factory battery died.  On something like a Tuesday I
noticed that it cranked almost imperceptibly slower than normal, and I
thought "I'd better have the battery replaced when I have the car in next."

On Thursday we had driven an hour away and when we go to re-start the car,
it won't turn over.  After trying a few times, and waiting a bit, we
finally get it to start and can drive it home.

My theory is that we just experienced the long tail of the bathtub curve --
the cells started degrading fairly quickly.  We hadn't run it out of juice
over its lifetime, which might have contributed to the sudden drop instead
of a more gradual decline.  Draining a led+acid cell damages it quite
dramatically, but might have also resulted in it slowing down while it was
still in the more horizontal part of it's degradation curve.

Anyway, I'm not entirely surprised that it died that way.

As far as why you could drive it once you started it: you were running off
the alternator, not off the battery.  If you had a big stereo that could
out-draw the alternator at idle, it might have been even more fun of a
trip.  ;-/

Sean
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