Since owning this car I have been reading up on its maintenance, the BlueTec System and complicated electronics. I am not worried about the actual engine.
Now that my wife and I are retired we will be driving it a lot to our vacation home in Florida.
Consequently I want to make sure that I am prepared to handle certain emergencies and not get stranded for simple things
For example, I have extra fluids, a tire repair kit, the goo in a can, and a heavy duty air compressor for those monstrous 21" tires.
However, my research indicated that the one thing that can leave you stranded is the death of the Auxiliary Battery.

This itty bitty12v battery is extremely small (approx L=3-3/4", W=1-7/8", H=2"). Mercedes Part # N000000004039.
However, it packs a punch. If it dies (you get a failure notice in the main display) you cannot shift the transmission.
Translation: You cannot drive the vehicle or put it in neutral (if it was stopped in park) even to get it onto a flatbed.
This battery's MAIN FUNCTIONS are (1) supply juice to the Electronic Gear Selector and the ECO System (Start/Stop).
BTW, the more you use the ECO System the more work is put on this battery thereby reducing its life. Mercedes suggest 4 years is a good run for a battery.
There is also a 10A fuse (#270) that if it blows you're also kaput.

My car is 4 years old (new to me). In Canada, Mercedes wants $138 (tax incl), however I got a slightly higher output battery (1.3 vs 1.2 AH) from Amazon for $20.
Not to worry (purest folks), the MBZ was made in Taiwan, not Germany.
Labour estimated at 3 hrs so at the dealer you're looking at $500.

The location of this battery is quite controversial if you follow what is written on the net.
Hence, my choice of words for the title of this thread to assist in future searches. I will of course include pictures.

My beef with Mercedes. This battery is so important yet they buried it. I am a retired engineer (35+ years in a nuke plant) and it makes no sense other than to gouge owners.
Underneath the right rear seat is one of the fuse boxes (F4) and all you need to do raise the seats and remove a plastic cover to gain access.
They could easily have put a cover like they did on F4 and not require complete removal of the left side rear seat back.
Also behind the rear seats is a 6" wide almost empty tunnel and all that would have been required for access would be removal of the two hold down hooks.
Next time I am in there I will relocate mine by lengthening 3 wires.

To add to this, when I got to my battery and performed a load test the battery failed.
It indicated 12.7V but was at the end of its life. It indicated that its lifeline was the main battery and as such if that had failed (left interior light on or something) I would have been stranded.
It indicated it was only good for 12 CCA out of the new spec of 160 CCA. On the flip side the Amazon battery indicated it produced 113% of the 160 CCA (after charging it with a 750 mA charger

 

Location of battery

 

Mercedes Part # N000000004039

12v, 1.2 AH, 160 CCA

 

Great post, thanks for the time and effort.

 

do you glow at night Just kidding thanks for the informative post and pics

 

My understanding is that the Aux battery is located next to the main battery under the passenger seat.
i have seen seen this verified with instructional YouTube videos.
What year and model vehicle do you own? What country are you in. Thanks.

 

Don't just look at the title of the videos. Watch them and listen to the description to find out later that it is on an ML or a 2015 GLE or earlier model etc.
None fit our vehicle GLE 2016 +
My signature and avatar tells you what I own (2016 GLE 350d Coupe) and that I am in Canada.
Canadian cars and US are basically the same other than Emission (Calif), use of KPM (not MPH) and L/100Km for MPG calculations.

For your benefit, here is a picture of the Main Battery which is located underneath the Passenger front seat.
In our vehicle this is also the location of the Battery Pre-fuse F33 panel.
Trust me, there is no space in there to put an Aux Battery. Changing that main battery will be a knuckle busting job with 1" space all around.

The following are actual pictures from my car

 

Only when I wear a certain ribbed .... oh never mind, let's keep it clean lol

 

Hessank,
Merci pour l’information. Je vais gardé pour l’avenir. Bonne journée!

I have another question: You bring up the eco start/stop system but we don’t have that on the 2016 GLE 350 SUV- US cars. Do you have that on your car?

 

Glad to help.

 

I know it was under the rear seat driver side (Left hand drive) on the 2016 GLE. It's funny that I got allot of response that there telling me it's in the rear cargo area behind the right side panel.

 

Lucky you. My car has it as well as my daughter's G
Don't know if it was an option to get or not.
Personally, I hate it and turn it off as soon as I get in the car. Others have paid $$ for an expensive module to de-program it from the system.

 

As an aside:
The reason we don’t haven’t in the US on this model is because it didn’t affect the fuel economy. This was written up at the time by the car magazines.

 

Thanks for the well written DIY tutorial and heads up on this "weak point" and to be prepared to deal with it if it comes up.

The ECO start/stop is a questionable stop gap "feature" and will go the way of "auto seat belts" I believe as hybrid designs/48V systems become more mainstream.

 

I have the Eco-Start/Stop on my GLE400. I'm in the USA. I'm about to bypass once I pay off my SUV (In the next few month).

 

I've been looking for a reasonably priced tester now having a travel trailer battery I want to keep tabs on as well. I looked up the model you used here and while I don't think I need one with a printer I'm wondering how it properly tests small batteries like these in the SUV's if they say they start at 100 CCA. With your background, while this is a nice featured tester that works with multiple battery types, is it testing the battery like the aux one properly? - Just keeping my options open on which model battery tester to consider since my auxiliary battery is now over 4 years old.

 

John I use that tester on all my cars.
Last winter the CTEC charger died on one of my cars and killed the battery. I re-charged it ran the car and then tested the battery. The Tester indicated that the SOH (health of the battery was only 60%).
I took the battery out and returned it to the store. They charged it and after a load test they found the same indication. So that was verification for me that the Tester works.

With the stay at home and finding things to do to stay busy I decided to change the Aux Battery on the GLE because of what I read. As the photos indicated above it said the battery was actually dead and was on life support from the main battery. As I noted, had the main battery died I would then be SOL somewhere. The new battery from Amazon indicated it was at 113% capacity.

This Tester works for me. The Aux Battery is a 160 CCA. I don't know how it will work for a one with a lower rating. The Printer portion never really printed anything useful. You don't need it.

 

Thanks, that's helpful. I thought I read somewhere the Aux. battery was a really low, or non-rated, battery of the type found in emergency exit lights. I like testing even the Gold Wing battery once in a while to stay ahead of battery failures. I may compare brand features to select a model down with similar features just without a printer if it works out that way.
You put out a lot of useful information in this topic I'll have to spend more time going over since I plan to handle all vehicle battery replacements myself.

 

Looks Like you're like me and do preventative maintenance.
I worked the past 37 years in a nuke plant so for me its in my nature.
So here's the wiring diagram of the Aux Bat (G1/7) showing the relationship to that fuse (#270)
and the ECO Switch (G1/13)

 

Where did you get the wiring diagram and information from? I went with an electronic manual from a vendor on Ebay I never got to work. One of these days I hope to have it or something similar working for general repair information.

 

I bought my manual from "Manual4You (no affiliation). It was also convoluted and wasn't simple since I can only view it via
Oracle VM. Took a while to get it going. Its still a pia and I definitely don't recommend it. Way too much work to get the simplest info