I think my beetle has a current drain which flattens the battery, but I'm not sure where the problem is.

The charging system is working: when the motor is running I get 13.9V at the alternator and at the battery, and the alternator warning light works while starting and then goes out just like it's supposed to.

I then turned the motor off and disconnected the battery negative terminal, and used a multimeter to try and take some readings. This is what I found:
I tried to measure a current passing between the negative terminal and the negative lead, but it didn't show any.
I measured the resistance too, and got -50ohm (this is probably the stereo???). When I switched the multimeter connections over I expected to get +50ohm but instead I got a blank reading which I thought was odd.

Where is the current leak likely to be???

With every thing turned off there will be no power demand, thus no current flow. The little bit of power required by the stereo to maintain the memory is probably too low for your multi meter to read.

Not sure what the -50 Ohm means, you cannot get negative resistance, it does not have polarity like voltage. It is probably just the way your multimeter displays.

What was it that made you think you had a current drain in the first place, describe the original problem which caused you to start checking.

The battery goes flat if I don't drive for a few days! It's a newish NRMA-supplied battery and the weather is very warm, so I doubt if there is a problem with the battery.

Dissconnect your battery +ive
Set your multi-meter to AMPS (not ohms)
Red lead to battery terminal and Black lead to cable.

What does it read now?

Now, is there a glovebox light?
A bonnet light?
An engine lid light?
Interior light?

Unless the battry is buggered, (and just because its newish does not mean it has not fallen over) there should be a significant drain to flatten a battery in a couple fo days.

Id look at the radio to make sure it is actually turning off.

The next thing is some kind of fault in the alternator/regulator. And the battery is earthing via a short in there but still allowing your alternator to charge at full voltage.

have fun
L8tr
E

Be careful withg useing you multi meter in amps, as most will have a fuse ciruit and a unfused ciruit. depending on the brand will depend on the max current the multi meter can coupe with. Sometimes the alternator can develope a short internally, and this will allow the alternator to use the stored eneregy. To test the battery condition (if it is not sealed) grab a set of wire and use these on the end of your probe, and meter between the cells. this will tell you whether you have a dead cell. so start with the negitve to teh first cell (ie into the electrolight) this shoudl read 1/6 of the total voltage (ie if battery at 12.3V then one cell (or each cell rather should be approx 2.06V. if all are within each other then the battery would seem fineish.

Cheers

Where were you measuring the resistance? You can get those kinds of readings when you accidently measure resistance across a battery. You could also have a faulty meter.

My guess is a dead cell.

OK I did a bit more measuring today: there is a current drain of about 35mA, which is presumably going to the stereo. I doubt if that is enought to drain a battery, even in a couple of weeks.

The battery is sealed so I can't test individual cells.

[ Edited on 3-2-06 by Purple Martin ]

call the nrma
get them to check
i bought a new battery recently and 6 weeks down the track it was dead.
repco replaced it on the spot fitted as even though i bought it at supercheap.

maybe even go to repco purple lol

I might call the NRMA, they supplied the battery! So they can replace it for me for free

any dealer of that brand will simply barcode it and see the wty tenure and replace for good will.