Battery problem - whats going on?

I have a 2000 528I
a couple of months ago I started having a problem with the battery going dead. I had the alternator and the battery replaced.
Everything was working great for two months.
Now, THREE times in the past two weeks, I go to start the car and "click click click click" the battery is dead.
I have it jump started and it works great for a week or so.
Where should I attempt to troubleshoot this?
Defective Battery? Defective Alternator?
Something else?
Thanks Jeff
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Jeff wrote:

Jeff,
There is probably a constant current draw. You need to troubleshoot it.
In my case, the dome lights were the problem. But you might pull one fuse at a time, with the car not running, and put an ammeter in place of the fuse. You may find one circuit is on all the time. Maybe it's the trunk lights or the glove compartment light. You won't know until you make some tests.
Bob
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Okay, when you park the car, the alternator light isn't on and the car is fine. But a day or two later the battery is dead.
This is the sign that something is pulling current while the car is not in use. Disconnect a battery line and put an ammeter in there, and see how much current is being pulled with the car turned off and the doors closed. If it's more than a few mA, pull out fuses until you find the culprit. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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OR the batttery has a short and is draining itself.
Disconnect a battery line and put an ammeter in there, and see

Good test, but do not exclude the battery itself from being the source of the draw.
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I said in another post that you could be having trouble with a shorted cell in the battery, but the thought just occurred to me -- you could be having a short in the starter.
I have an old Jeep CJ5, and the clicking thing started. I kept getting the charger out, and jumper cables, to get it going, but eventually the cables would not do the trick. Anyway, I finally came to the conclusion that the starter itself was shorted, and it would cause the starter solenoid to fire (the gear would be thrown into the flywheel), but the starter motor would not spin.
I think your more likely suspect is a bad battery and/or a load that is active when the car is parked, but do not forget the starter itself can cause the symptom you reported.
Voltage is a function of load. If the voltage is low, the load will not be driven. If the load is high, it can pull the voltage so low that it can not drive the load.

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On mine, I had a sticky passenger door lock. If I locked the car and the passenger side didn't go down fully, it would drain the battery within a day.
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