In this video I answer these questions: What is the Auxiliary battery used for? Why does it fail? How to replace it?
If you’d like to jump right to the answer:
0:49 What is the Auxiliary Battery used for?
1:30 Why is the “Auxiliary battery malfunction” message displayed?
2:21 How to replace the Auxiliary Battery?
This is the same repair process for all 2007 2008 2009 2010 2011 2012 and 2013 Mercedes-Benz S550 w221.
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Thank you! Just saved $350 because of your video. This was awesome.
Do you you know how to unlock car when battery dies. ??? Valet key doesn't work. I don't have a battery in trunk.
Could you please tell me exactly where the Aux. Battery is located on S550 W4M, 2013 model please. Is it where this video shows?
Where can I find the auxiliary battery ?
Very good video instructions. Thank you.
I bought an aftermarket battery based only on looking at various photos and 12V 1.3ah spec as I couldn't find any information on the physical dimensions. So, taking a risk, I ordered one from Amazon.
From watching your video, and using the orientation when you put the battery next to your multi-meter, I noticed that the Positive terminal is on the left side of the battery looking from the terminal end of the battery. The one I ordered from Amazon has the terminals reversed.
WILL THERE BE ENOUGH SLAG IN THE WIRING TO ACCOMMODATE THIS SITUATION WHEN CONNECTIING THE TERMINALS?
WOULD THIS CAUSE ANY PROBLEM?
Also, perhaps if you can update your video with the exact dimensions of this Auxiliary Battery, this will help other to confidently buy an aftermarket battery.
I hope to have an answer from you before I start pulling things apart to replace the said battery.
That was pretty Good
Very nice video and right to the point. Can you post link where to order factory battery from? Thank you.
Question, I know this is a year old. What if your aux battery was just changed for a new one, but 50% of the time when you start her up you get that light again…then i shut it off, open the door and start it back up and the message goes away. @Jamie'sGarage
Avery good information
My 2011 S550 doesn’t show a Auxiliary Malfunction on the display- i just change my main battery thought and my AC doesn’t work as strong as it did before I changed my main battery. I was told the the Auxiliary battery is also used for the AC radio etc. Do I need to change the Auxiliary battery or is there something else wrong?
I replaced mine with a brand new one but it still illuminates the "auxiliary battery malfunction " on the dash, thought the new battery might be bad so bought another one and same thing…can someone help please??