04 Passat battery drain?

Not twice in the same week. To reduce the battery drain to a min the car should be locked so the alarm is set. I'm going to make a guess and say the radio or radio amp, if it has one is causing your drain.

NO, once the key is off, it's off and I think the newer radios turn themselves off after a certain time limit. But I have seen amps that cause the drain. The difference between locking the car is about a 5-10ma reduction in draw.

I would get access to an ammeter (most multimeters have such a function, but check the fuse first; many have the meter fuse blown thru mis-use previously). Turn all car things off. Attach the positive probe to a chassis ground. Hold the negative probe to the negative battery terminal while removing the negative battery terminal.

If you are successful at maintaining continuity thru the meter while the battery terminal is loose, you will not have to reset the alarm, clock or radio. The continuity will be maintained thru the meter.

If you read more than 20 ma draw, troubleshoot further. If you have less than 40 ma draw, replace the battery. If both, do both. Note that these numbers are off of the top of my head and are not standard go/no-go tests.

You can try putting the key into the ignition and/or locking the car to read the difference. But a 40 ma draw should not drain a car battery in a week.

Put the battery terminal back on, and then remove the meter.

How do you connect meter leads to chassis and negative battery connection while removing and reinstalling the battery terminal? Alligator test leads are useful, but it could also be done by 4 coordinated hands.

Other things that might happen:

You could blow the meter fuse if the load is bigger than the fuse rating.

You could lose contact for a bit and have to reset things.

All the computers draw a slight amount of current when turned of. Such as the engine & trans ECU, clock, radio, window ECU, etc, etc, etc. If you don't lock the car, then it should live several months, maybe longer before the battery gets drained to the point it can't start the car. If you lock the car that kinda puts everything to sleep to save battery life. I'm told even after so long the anti-thief red LED even stops blinking. Never been told how long that is. MY 99 Passat sets in my garage unlocked and key in ignition and I never had problems even after several weeks. As for your car, you got a problem and I think it's going to be a faulty battery(un likely) or like I said before it's the radio/amp.

Correct, most VW's fall in the 14-20ma windows except the NB which is near

30-40ma depending the year, engine, options. Still at 40ma draw it would take a long time to kill the battery. If some electrical math wizard want to do the math for how long a typical battery can last with 40ma please do.

Figuring a car battery is maybe 40 to 60 amp hours, we could easily lose 20 amp hours and still have a lot of power to start the car.

20AH =20000 ma-hours. So 20000/40 = 1000 hours. 1000 hours/ 160 hours/week => 6.25 weeks.

Correction: So 20000/40 = 500 hours

500 hours/ 160 hours/week => 3.1 weeks.

Now normally the draw is less than 40 ma, and the battery can spare more than 20 AH, so normally it lasts longer.

If you are lucky enough to get the car when it's acting up, I have pulled the radio and found the heat sinks to be very warm after the radio was off all night. Same goes for amp.