Tracking down a battery drain

[Joshua Van Tol]

450 mA standby current draw is too high, you should be seeing well under 100
mA, preferably less than 30 mA.

A typical car battery has 40-60 Amp hours of capacity. At this rate, the
battery will be fully discharged in:

50/.450 hours = 111 hours = 4.6 days. It'll probably be discharged enough to
make it hard to start in about half that time. If you don't drive long
enough each time you're out and about to re-charge the battery fully, after
a few days to a week, you'll have a dead battery.

500A is fine. I wouldn't have replaced that battery unless it didn't crank
well at cold temperatures.

You're going to need to do the test with the ammeter or test light as others
have recommended. An important thing to remember is that if you've got the
door open (to access the fuse box) you'll need to tape down the door switch
so the dome lights don't come on.

If you don't do this testing and fix the cause of the current draw, you'll
be on your way to wrecking this new battery within a few weeks.


On Wed, Sep 29, 2010 at 11:22 AM, <TooManyAudis at aol.com> wrote:

> Took the car to Advance Auto last night, had them do a charge on  the
> battery, then a system test.
>
> Existing battery (4 years old -- Huw incorrectly guessed at its age being 6
>  years, resulting in 4 demerits) was putting out 500 +/- amps, with it
> being  rated for 700 amps new.
>
> Put in a new battery for $100.  Rated at 850 amps with 700 cold  cranking
> amps.  Started strong this morning.
>
> The salesman at Advance did a charging system test after the install of the
>  new battery.  Results are:
>
> 1)  Battery:  12.56v; measured at 817 CCA, rated at 700  CCA;  Temp:  79
> degrees f.;  Good Battery
>
> 2)  Starter Test:  Voltage:  10.99v;  Amps:   215.8A;  Time: 1.03 seconds;
> Cranking Normal.
>
> 3)  Charging System Test:  No load:  14.00v, 4.4A;   Loaded:  13.47v 2.4A:
> No Problems
>
> 4)  Drain Test:  0.45A:  Pass
>
> With # 3, my Instrument cluster voltmeter showed right around 12v with  the
> high beams on and AC on max during this test.  Is there an explanation  for
> the difference.  Is the IC voltmeter picking up voltage after the  radiator
> fan, blower fan and compressor clutch?
>
> Also, with #4, is 0.45A too high?
>
> Thanks for the help.
>
> Tom
> Charleston, SC
>
> 1995 A6q  5-speed (up for interesting offers) 249k
> 1988 80q (sold, and still going  strong!) 250k+
> 1991 200q20v towed away in the middle of the night by a VW  diesel pickup
> 275k+
> 1985 4kq a freakin' beast of a car! 275k+ and presumably  still going
> 1987 4k died in a hit and run 250k+
> 1983 4k Very first Audi 35  to 38 mpg.  Victim of crank key failure 300k+
>
>
> In a message dated 9/29/2010 9:29:32 A.M. Eastern Daylight Time,
> glenahan at vfemail.net writes:
>
> so why  guess? Measure the idle draw,and load test the battery. 20:1 its
> the battery.  6 yrs is 2 beyond its shelf life.
>
> Grant
> On Sep 28, 2010, at 4:14 PM,  Steve Buchholz wrote:
>
> > I'm with Huw ... the voltage you're seeing  should be enough to crank ...
> likely high internal resistance in the battery  is the problem.
> >
> > I'd also allow a bit higher battery draw with  everything off ... 10mA is
> too low IMO, I wouldn't worry until the current got  up into th 100mA range
> ...
> >
> > Steven Buchholz (mobile)
> >
>
>
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