Hi All,

Just wanted to share my weird experience. This summer I had taken on the ambitious project of installing an Android Head unit from China in my car. The project was every bit as hard as I expected and quite a bit more; without a wiring diagram and any support from the company at all, I had to rely on YouTube videos. But alas, the job did indeed got done using YouTube videos as my teacher. You can see my DIY on a separate thread (still have some loose ends but mostly there).

Back to the parasitic drain issue. While installing my head unit, I forgot and left door open and completely killed the battery. So I bought a new battery, but the car continued to totally die in about 7 hours. I suspected parasitic draw, and measured about 50 milliamps, which is a draw but should not kill the battery in seven hours. For a separate issue, I took my car to the stealership and they said there was no significant parasitic draw..

Perplexed, and out of necessity, I installed a kill switch in the trunk to preserve battery while my car was not being driven. But I found it too tedious to unlock the trunk with the key to turn on the kill switch to power on my car. So then I found this Bluetooth kill switch on amazon, which I bought and installed. It seemed great at first, since it came with a FOB to turn on and off the car.

But my battery and voltage issues continued. And got worse. The AC and radio would randomly cut off even though battery voltage was sufficient. At one point, my wife was in the car and she got really mad and said I "always" broke my car. It sucked.


So one day I posted to my "MB Fanatics" group on Facebook, and one person commented that the auxiliary battery was probably shot in my car. I had not thought of this since I thought this battery solely was a backup for the SBC brakes. Upon further research I discovered that the aux battery actually supplements the voltage in the car as well as powers devices such a AC, SBC brakes, radio, etc.

Then I bought a new aux battery from FCPEuro.com. When I went to install the new battery I discovered that the existing battery was trashed. It was leaking and was clearly gone. When I put in the new battery, the car ran much better, but still not as strong as I would expect.

Now I thought that I probably killed the main battery so many times, I had better replace that as well. Although the main battery was only a few months old, after completely draining a half dozen times it clearly had to have been shot as well. I went back to Advanced Auto when I purchased the battery and got a new free battery under warranty.

When I put the new battery in, the car still didn't start as strong as expected. And the AC continued to turn off.

That's when I took off the Bluetooth Kill Switch. I had not considered this before, because it seemed to work well, but this appeared to be the missing link. When I took off the Bluetooth kill switch, my car started with mighty authority.
At last problem solved (I hope). All this misery and domino effect from installing my Android Head unit.

Lesson of the story is to always disconnect negative battery terminal when working on your car; if had had done this it would have saved me from immeasurable suffering..

 

Thanks for the diagnosis.

I don't know if this is a complete lesson. It appears that your trashed aux battery was contributing to your problem. The Bluetooth remote disconnect was another contributing factor. So, Lesson #1 is disconnect the main Battery when working on the car for any length of time to prevent discharge. Lesson #2 is to check all batteries in the car for their condition should you be having strange inexplicable problems. Lesson #3 trust MB engineers and don't ad gadgets in series with the main power conduits.

 

Yeah buddy, I learned all three lessons the hard way. I did connect a battery maintainer/battery tender/trickle charger, hope that won't be an issue :-)