Audi A4 B5 - Do I have a flat battery?

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Sun 26 Feb 2012 19:29
Audi A4 B5 - Do I have a flat battery? - garethgas

Hello, I wonder if anyone can offer me some advice?

My Audi's battery is running flat after 3 or 4 days of not being used. I've checked the voltage (12.88 v) and removed the neg and am getting a zero reading when testing amps. When the engine is running I'm getting over 14 v

The battery is only 16 months old and this problem was there when I bought it but I used it a lot more then so it wasn't really an issue although I keep it trickle charged during the week in case I get stranded.

Any ideas of where to go from here?

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Sun 26 Feb 2012 19:44
Audi A4 B5 - Do I have a flat battery? - Quicksilver

Check the blocking capacitor on the antenna embeded into the rear window(s).

Disconnect the wires and see what difference, if any, it makes.

I had this on a Sharan once. Took the garage ages to fix it. Had two batteries replaced when it was nothing to do with the batteries.

Q.

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Sun 26 Feb 2012 19:48
Audi A4 B5 - Do I have a flat battery? - garethgas

Thanks for your quick reply. I'll have to dig out the Haynes manual to see where that is and check it.

However, if it was faulty, wouldn't I get an Amp reading at the battery or wouldn't it register?

My puzzle is that I'm not getting any current loss whatsoever, I was expecting a few mA at least

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Sun 26 Feb 2012 21:49
Audi A4 B5 - Do I have a flat battery? - Quicksilver

Are you sure you do not get any current flow? What kind of meter?

A faulty capacitor will show up either as an open circuit, (OK no leagage) or a low impedence, (resistance) of a few hundred ohms, (or less!). Mostly they fail with low impedence.

Have you put the meter in series with the battery? With the battery positive disconnected and the meter bridging the circuit between the battery connection and the feed cable?

Even with no fault i would expect some "keep alive" leakage current in the range of at least 100uA to 500uA. I am very surprised you do not have anything and I do not really believe it.

Another potential failure could be the rectifier diodes in the alternator. One or more of the phases could have "leaky" diodes.

How about some hidden interior light like boot or glove compartment not switching off\?

Q.

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Sun 26 Feb 2012 22:13
Audi A4 B5 - Do I have a flat battery? - garethgas

Thanks again for your reply. I'm using a digital multimeter (fluke 75).

I connected the meter from the neg post of the battery to the disconnected neg cable. I left the pos connected.

As you say, I expected some current loss for the alarm etc but zero suggests I'm doing it wrong.

I checked/removed the obvious bulbs as plan A but the fault still there.

If I disconnect the alternator and left it for a few days would that test the alternator/diodes?

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Mon 27 Feb 2012 07:57
Audi A4 B5 - Do I have a flat battery? - elekie&a/c doctor

No modern car has a zero parasitic drain.Your meter connection is correct,so iI would suspect the fluke is at fault .Don't forget you need to move the red plus lead into a different connector on the meter for amps/mA reading.I would expect a draw of between 60 and 100 mA after approx 30 mins stand time to allow for all the ecus to shut down.hth

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