Battery dies fast.

[Multibeemer]

Here's the procedure described by eHow.com, but it leaves me with a ton of questions, which I've added in square brackets:

Drain
By an eHow Contributor

When a vehicle battery won't maintain a charge, it's possible that you're dealing with a parasitic draw. Testing the battery is the only way to find out. To find a parasitic battery drain, use the process of elimination to narrow down the problem.

Difficulty: Challenging [Great...]
Instructions

things you'll need:
Battery tester with 10-amp DC range [I'll have to get one of these, as my VOM only goes up to 250 mA]
1
Charge your battery if necessary. Dead batteries (and even weak ones) don't give accurate results on a draw test. The dome light is a good indicator of battery strength. If the light is weak, pulsating or refuses to turn on, you'll need to charge the battery.

2
Shut off everything in the car. Pull the keys out of the ignition. Ensure all service lights are off, lighted compartments closed and doors shut. Open the hood, and disconnect the trouble light underneath if your vehicle has one. Wait for 30 minutes before moving on to Step 3. (This enables normal drain from interior components to finish cycling.) [How do I do this, given that the battery is in the luggage area?]

3
Set your battery tester to 10 amps DC. Disconnect your positive battery connection (red cable) and position it safely away from metal components. Connect the meter's positive probe to the battery's positive post while simultaneously holding the negative probe in the air; keep it away from anything metal. [Some on this forum have said not to disconnect the cable from the battery (not sure why...)]

4
Place the negative probe on the end of the removed positive cable to complete the circuit. Yes, you're putting a negative on a positive. Yes, this is ok. If you have a severe drain, you're likely to pop a fuse or two-identifying your problem.

5
Check the meter reading. A normal reading is usually under .035 amps. If you have a minor drain that causes a higher reading, you'll need to check each component.

6
Remove the first fuse in the box, and check to see if the load problem is resolved. If not, replace the fuse and check the next one. Repeat the process with all fuses. If the fuses check out fine, you have a wiring problem.

7
Remove the tester and reconnect the battery. Follow the hot wire to the next connection. Remove the positive cable and connect the positive probe of the tester in its place. Connect the negative probe to a metal object. Check the meter. If the drain isn't resolved, reconnect as normal and follow the hot wire to the next connection. Repeat this step at each connection point until you narrow down the problem. [I assume removing one fuse at a time in an alternative way to do this as I don't understand what he means by "Follow the hot wire to the next connection"]

[JCL]

Originally Posted by Multibeemer

So, back to my original question - could somebody who has done it please explain, step by step, how exactly to troubleshoot the source of the current drain in these cars? Specifically, how do I deal with the fact that I have to open the hatch, thus setting off all the interior lights, to get to the battery, and what's the exact procedure for dealing with the need to let all the subsystems "go to sleep", which is connected to the interior light problem? Do I have to get in the car, shut all the doors, crawl in the back, and do the procedure (of which I've read several different versions)? Am I making this more complicated than it is (probably!)? Thanks.

You are making it more complicated, but only due to lack of basic troubleshooting skills. You need to have the right tools, you need to know how to use them properly, you need to know how the system being diagnosed is designed to work, and you need to deal with issues as they arise. It isn't reasonable to have a very detailed instruction list, IMO, as you need to do the troubleshooting. Troubleshooting is based on doing small tests, finding results, and taking action based on those findings, going on to the next small test. It is like a fault tree, and you have to work through it. You need to solve little problems along the way, like how to get access to the battery.

I would assume that the rear hatch is open, and you have got the interior light off, however you accomplish that. Then you need to have your probe-type ammeter ready (I assume you didn't buy the inductive clamp-on ammeter we discussed some time back). connected in parallel with the earth cable. Then you need to disconnect one end of the battery earth cable, making sure not to open the circuit. The ammeter acts as a part of the circuit. You can use a jumper wire to make this easier, but you can't just take the battery cable off and then measure the current between the cable and the post, since you will have done a reset by virtue of opening the circuit.

You are looking to get it down to 35 or 40 mA after 16 minutes.

I suspect that your challenge won't just be reading the ammeter, but isolating individual circuits to see what changes. There are a lot of combinations and permutations. There are multiple fuse locations. And this is best done by a technician who has done it before, and knows what is likely to be a cause (because of knowing how the vehicle is wired).

For an overview, read this article on an older model BMW. It has step by step instructions.

BMW E38 Battery Drain

Good luck.

[Multibeemer]

JCL,

Thanks for the step-by-step procedure; that's what I've been looking for. I realize that tracking down the source of the leak is the hard part of the task, but I was stuck at the step of how to even hook up the meter, so hopefully now I'll be able to at least get a reading, giving me a chance to track down the source.

[theblue]

what was the final outcome? (if you're still around here)

[diyanich]

I wasn't able to find a significant draw during a few tests I performed,I am sure I wasn't able to do that properly though.Because every time I disconnected the battery for a long time,in some occasions for longer than 3 days,battery was charged good in no time and cranking like a beast,but....but in a week or so it was becoming a lazy bitch.
I had telephone and a hitch harness fuses pulled,both in the right rear compartment.
Why a hitch on e you may ask,I answer,one of the prongs in the connector is broken and I could see an excessive oxidation.So I pulled it.
Do you lights come lit when you crank? Like brakes,ABS,Traction Control?
When my starter spins slow I have all those coming.When it spins well only a brakes (!) one and when fully charged,no light.It's not happening on my friends 2005 4.4,so I suspect that my discharge relay is stuck from time to time.Just a guess.
Also,driving with A/C on makes my battery to get a strong charge no matter how short distances are and how often I am cranking.
I am sure that there's no just one cause and I think I have eliminated a couple by replacing FSR,pulling those fuses.
Get yourself a charger,with a desulphator function,better an automatic one,it's gonna keep your battery at an optimum performance.
I know that some people won't agree with me,but maybe an OE battery is a better idea?

[theblue]

thanks for the update.

[Multibeemer]

Originally Posted by theblue

what was the final outcome? (if you're still around here)

Not sure who the question was directed to, but my experience was as follows: I found a good youtube video which explained how to check for an excessive current draw. I followed this procedure, and isolated the problem to the circuit protected by one particular fuse (I believe #72, but it's been a long time). I then found a wiring diagram for the vehicle, and determined which components are in this circuit (the stereo/nav, and the rear CD player, primarily), so I systematically disconnected each of these components, plus the video screens in the head rests for good measure, and wasn't able to reduce the size of the drain. So, I punted and installed a relay in the circuit which is energized (completing the circuit) when the ignition key is on, but shuts down the circuit when the key is out of the car. I realize this doesn't actually solve the problem, but it's worked like a champ for over a year (I can let the car sit for weeks on end, and it cranks like ti was just charged), so I'm happy.

[diyanich]

So,here my question...
Why do the modules need to stay awake?
What is the point?
Can anybody explain it?