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..

 

Hi,


This is interesting as I am potentially in a similar boat here. I just bought a 2006 CLS350 with 90k miles. The main battery in the boot seemed really poor and I was continually getting the "extra functions disabled" type message on the dash. This culminated in me having to get a jump start one day so first thing I did was go buy a new battery.

Anyway today after being away from home for 4 days I went to start the car and it wouldnt crank at all. I have just swapped the battery out and it all seems good just now. However the car also came with a custom android head (Wonderfoo PX5) unit installed and I'm wondering if that was potentially the reason for the old battery draining. Whats the best way to check if the head unit is draining power whilst everything is switched off?

 

Good question! Remove the fuse for your radio located in drivers side fuse box.. If drain stops that is the problem. More likely, as I discovered, the hard way, is that if your main battery died then your aux battery also needs to be replaced. The two batteries are on one circuit and of one is bad the total car voltage will be low. The aux battery is really easy to change too. It is worthwhile to change the battery either way since this is the back up for your electric SBC brakes. You never know the last time it was changed. Feel free to PM with further questions..

 

Hey buddy,
After 6 days of being away I came to find my battery dead too. I also have an android head unit. Did you figure out your problem?? So frustrating!!

 

Change your AUX battery.

 

I had a battery drain for 3 years on my SL, I spent months trying to figure it out, finally I pulled the low mile alternator and had it bench tested, passed at Auto Zone, took it somewhere else , the guy let it run longer and it failed, had a bad diode causing battery drain after car sits for a week, now car can sit for months and no drain!