In rec.autos.makers.vw.watercooled, D&LBusch wrote:

>I have an 04 Passat. I usually leave the keys in the ignition when I park
>it in the garage. Lately the battery drains and requires a jump (twice in
>the last week). Does leaving the key in the ignition cause a batery drain
>due to something else running that I am unaware of? Thanks in advance -

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.