Battery Drained on 100CS Quattro Wgn

[Brett Dikeman]

At 10:17 AM -0400 8/2/03, Barry Lampke wrote:

>Something is draining the battery on my 92 Wagon.

How fast?  Overnight?  Few hours?

>   What's the best way to determine what's draining it?

This assumes nothing is wrong with the battery itself- cells can
short out, for example.

Hook up a test light(or a voltmeter with a HIGH ENOUGH CURRENT RATING
on its ammeter function) in SERIES with the battery, ie between a
cable and terminal.  If you've got a drain, the light lights up/meter
shows current(on the voltmeter, you should not see anything over more
than about 100 mA, maybe slightly more on a car with an aftermarket
alarm, lots of dodads, etc).  Now, start pulling fuses from the
fusebox one at a time, and look for a big current drop.  Tada, that's
the suspect circuit.  FYI, drain on the radio circuit and engine
computer circuit is normal.

Before going through all that, make sure the battery is OK; after
charging, with the "surface" charge removed(wait 2 hours or so after
finishing charging, with nothing connected), at 60-70 degrees F, you
should have a voltage of 12.65 for a 100% charge.  The link below
contains a chart which gives voltages+temperatures to indicate a
state of charge.

BEFORE CHARGING check the levels.  The level should be slightly below
the bottom of the vent 'tube' in each cell.  With a flashlight,
compare the colors of the plates. Is one cell's plate color very
different?(it will be noticeable)  If so, you've got a shorted cell.
Often the level in that cell will be higher than the others(since the
others are getting overcharged, and the shorted cell isn't charging
at all).

Shorted cells are most commonly caused by excessive charging rates;
violent gassing causes the plate material to pit and/or break
apart(it's basically a thick mesh for maximum surface area, not a
real solid plate) and the pieces of plate material collect at the
bottom of the battery.  If one happens to be large enough, it can
fall and cause a short between the cell's + and - plates.

Shorted out cells is one of the top causes of battery 'death' and
it's pretty much permanent without a LOT of messy, dangerous work
that is not even remotely worth the trouble; just get the battery
recycled.  The other cause is sulfation; this is caused by not
keeping the battery charged(sulfation starts after a week or two of
the battery sitting without a maintenance charger.  Faster if there's
a drain on it, like the car's ECU, radio, etc).

If you want to know almost everything there is to know about
lead-acid batteries, how to keep them happy, etc, an indispensable
site is here:

http://uuhome.de/william.darden/


B
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