W212 Auxiliary Battery What and Where?

[as400]

Having got my dashtop phone charger hardwired in by a local mechanic it has stopped working and in addition I am getting the old Auxiliary Battery Malfunction message.

Suspect this may be from the mechanics comments "i found a black box, looked like a tracker and took a live feed off that"...

Am hoping I can get the live feed taken from somewhere else but if I need to obtain a new aux battery when Google searching I am finding two very different looking things...which one is it for a 2011 W212 and is the location at the side dash entrance?

 

[KillerHERTZ]

From the HOW TO section. The Aux battery is located in your boot.

How To Change Aux Battery | HOWTO

My latest video, hopefully useful to anyone needing to change it: :)

forums.mbclub.co.uk

Will be the same for your car.

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[AMGeed]

The aux battery is located in the boot under the carpeting in the wheel well on the o/s.
It looks like the Fiamm one in your bigger image.
It's an easy swap over with nothing to code or reset afterwards.

 

[as400]

Hmmm thanks I will venture out in the morning and search in the boot area, if the aux battery is there I wonder what black box the mechanic connected to in the side dash area?

 

[mersum1es]

I answered other forum, that is backup for electric gear selector in steering rack (if exists). Aux battery definition is used for that and often for start/stop battery too, so specific SDS fault code should be pulled where part index number is shown.

 

[as400]

Quite an empty boot as far as aux battery goes, and no stop/start on this car.

 

[as400]

OK OK so thanks to mersum1es in Finland, still reading about this, so not every model gets the bigish aux battery in the boot like this, not sure what it does really, looks fab with the red leads etc..



My issue is with the tiny (well much smaller) battery that sits inside the side panel of the dash looks like



Apparently when this is feeling ill it also throws up "Auxiliary Battery Malfunction" message.

MBWorld.org quote

"The battery is for the electronic shifter in the event your main battery dies and the car needs to be towed. It also serves for some other functions like the brake hold feature. Parts guy at MB dealer stated it did not need to be hooked up to drive."

Suspect my chap hooking it up as a feed to power my phone charger has ensured it threw a hissy fit.

 

[as400]

Hmmmm

Mercedes-Benz Auxiliary Battery Malfunction Explained

Are you facing auxiliary battery malfunctions in your Mercedes Benz? Click here to have the detailed knowledge!

xenons4u.co.uk

 

[Yettie]

Hi I did the same thing, wired a dash cam to the small aux battery in the dash. Got the same message so disconnected it. Ran a feed from the rear fuse box. Problem solved and the message went away.

 

[as400]

Hi I did the same thing, wired a dash cam to the small aux battery in the dash. Got the same message so disconnected it. Ran a feed from the rear fuse box. Problem solved and the message went away.

Thanks Yettie good to know its not just me!...Was it easier to run a feed from the rear fuse box?...I haven't a clue but isn't there one in the front engine area?

 

[geoffus]

Why would your mechanic wire a phone charger rom the aux battery ?
Surely take the power from the cigarette lighter?

 

[AMGeed]

Quite an empty boot as far as aux battery goes, and no stop/start on this car.

View attachment 134949

Ah, I wrongly assumed your 212 had stop/start. Sorry for the confusion over the location of the Aux battery.

 

[Yettie]

Thanks Yettie good to know its not just me!...Was it easier to run a feed from the rear fuse box?...I haven't a clue but isn't there one in the front engine area?

Hi yes there’s one at the front. I am rather large and found it easier to route from the rear as I’d done that before.

 

[keith of kent]

I recently asked the location of the auxilay battery on my 212 and received a variety of replies not all of which were helpful. But one person told me to scan the QR code sticker on the n/s B post and it does indeed show the location of both batteries;also tried it on wifes GLA and found that it also has two batteries.
Very useful piece of information

 

[as400]

All's well that ends well. The mechanic found an alternative power source, message "Auxiliary Battery Malfunction" disappeared and phone is charging nicely from its magnetic Mount thing, so the power cable plugs into that, the phone Case is magnetic and just clips on via the magic of magnetism. Its made by Mous if anyone is interested and the magnetism does not interfere with NFC payments or wireless charging.

Should have asked him to swap out the battery for a new one as they are Cheap.

Still looking for a conclusive answer that only cars with stop/start have the additional battery.

 

[Diesel Benz]

...

Still looking for a conclusive answer that only cars with stop/start have the additional battery.

By "cars" you must be referring to W212 Mercedes cars, not all Mercedes models (definitely not all cars)? I'm afraid it isn't exactly simple even for W212 cars but ignoring the hybrid model, start/stop cars have the motorcycle size aux battery. Cars without start/stop have the small battery IF they have the electric gear selector (gear selector lever at the steering column). I though this was already mentioned but no conclusion is possible at the forums as the correct answer will always be followed by incorrect or incomplete answers.

 

[as400]

By "cars" you must be referring to W212 Mercedes cars, not all Mercedes models (definitely not all cars)? I'm afraid it isn't exactly simple even for W212 cars but ignoring the hybrid model, start/stop cars have the motorcycle size aux battery. Cars without start/stop have the small battery IF they have the electric gear selector (gear selector lever at the steering column). I though this was already mentioned but no conclusion is possible at the forums as the correct answer will always be followed by incorrect or incomplete answers.

So W212's without stop start will have two batteries (one regular and one small one for the gear selector) and those cars with three batteries will have the stop/start function. Seems to be the conclusive answer!

 

[Neiltodd]

So W212's without stop start will have two batteries (one regular and one small one for the gear selector) and those cars with three batteries will have the stop/start function. Seems to be the conclusive answer!

Pretty sure only 2 batteries but they will do the extra jobs required.

 

[Drewski09]

Nice one...

 

[Diesel Benz]

It appears to be too complicated to describe it properly. As Neiltodd says, no need for three batteries as the start/stop battery handles the gear range selector backup battery too.

Then there are single battery cars too. Not sure of manual transmission W212 was sold in the UK, it would not have any AUX battery. Neither the floor shift model (before start/stop era) has any AUX battery because gear range control is mechanical in this case:

FG 212.005 - CENTER SHIFTER CONSOLE, AUTOMATIC TRANSMISSION > EPC Online > WebAutoCats.com

Mercedes parts catalog. CENTER SHIFTER CONSOLE, AUTOMATIC TRANSMISSION. Spare parts catalog EPC Online.

webautocats.com