Dying Battery Issue: Tracing Parasitic Draw?

[ClassE]

Two part question:

 

-While I'm trying to sort through this dying battery issue, I'm planning to disconnect battery when car is not in use.  Does it matter which terminal I pull off - and why?

 

-Any suggestions on tracking down a parasitic draw while the car is parked?  No idea how to go about finding whatever is draining down my battery.

 

Background: Every time I park my car for a extended period of time, the battery goes dead. I can throw it on my charger which has a start feature, and it will start no issue and drive no issue.  If I drive it the very next day it seems to retain enough battery to start again, but if I leave the car for an extended period of time like a week or so it is dead.   I have a trickle charger that I normally throw on the battery when the car is not in use, but for whatever reason that does not seem to be doing any good anymore. I'm not sure if I can test the trickle charger to make sure it's working?   I would rather just try to track down whatever is killing the battery. 

[B C]

Connect an ammeter inline with the battery cable, note the current draw. Remove fuses one at a time to see which circuit has the current draining component then start checking items on that circuit by disconnecting harnesses, switches, and other components on that circuit. What aftermarket components do you have wired in besides the wideband? Any alarm or stereo amps?

200mA or less is the general acceptable amount of current draw

[Boris3]

Good advice from Snap. Sounds like you've already narrowed it down to the draw issue. But just to step back for a second, how old is the battery? You've already had it tested and tested/checked the alternator to make sure everything is output correctly when the car is running?

[GunMetalGrey]

Ensure the battery connection at the firewall is tight, I had some weird things going on before realizing the connector had vibrated loose. 
Other than that, do what Snap suggested. 

[straight6pwr]

some ones i've heard: power antenna, glove box or trunk dome lights, aftermarket radio, interior lights

On 9/18/2016 at 10:18 AM, Boris3 said:

Good advice from Snap. Sounds like you've already narrowed it down to the draw issue. But just to step back for a second, how old is the battery? You've already had it tested and tested/checked the alternator to make sure everything is output correctly when the car is running?

good point on checking the battery. depending on how long he has been battling this, the constant up/down of your battery charge could have worn down the battery, even if it was pretty new before this all happened. 

[andyhundley]

I had a faulty hazard switch drain my battery on my first E30 like 10 years ago. What a nightmare that was to figure out. 

[SGP]

I had the same problem, just fixed it yesterday! 

I used a multimeter with a milliamp scale between the negative terminal and the chassis with everything switched off.

There was a 74.2 milliamp drain. (it should be 50 or less) 

The next step is to remove (and replace ) the fuses one at a time, when you've removed the fuse that is powering the circuit responsible for the parasitic drain the milliamp reading will drop.

In my case the circuit was fuse 21. The interior lights, including the luggage compartment and the glove box. The rechargeable flashlight, the stereo system, the clock and OBC.

Anyway it turned out to be a "sticky hazard warning light switch, as per andyhunly above! This is one of the few circuits that stays live when the car is locked up.

After I depressed the hazard switch on and off several times to free it up (it now works properly) the drain fell from 74.2 to 14.2 ma - well within acceptable limits.

If the SI batteries are faulty / worn out they can also be a common source of parasitic drain. bavrest.com offer a great service for refurbished  instruments and SI boards