Michaelscai

I'm getting Auxiliary Battery Malfunctioning message. Where is the Auxiliary battery located and is it a DIY work to replace it? If not, what's expected cost of getting this replaced by MB dealer or a auto shop?

I hate it Mercedes have this Auxiliary battery - just another over engineered feature

Teckno

Lots written on this site.
NOT a battery, but a capacitor, in a black box about the size of a large packet of cigarettes !
Non OEM ones sold on eBay for around Au$80-120.00.
OEM here in Oz around AU$360 for unit.
It is hidden on passenger side, front footwell behind carpet, most probably up against firewall.
Simple unplug and plug new one in. No need for ODB11 reset, will reset again after few Km done.
One thing, charge your car 12v battery overnight and see if it re activates - some owners have noticed if the main battery is crashing due to age or short drives, the stop /start can stop.
The capacitor will fail over time, so I presume you are outside warranty. As it is not a battery as such warranty witching period will cover item and labour charges.
Allow around 1.5 hours labour fee.

Teckno

Try this link
http://www.opusivs.com/

https://uk.autologic.com/news/support-case-study

Michaelscai

If I look at the passenger foot well, I can open
a panel but just see fuse boxes

my exact model is 2016 Mercedes GLC 300

its insane to require so much effort to replace a auxiliary battery that I still don’t know where it is?

Teckno

The UK auto logic site has some photos and general guidance.
Removal of inside skirt, removal of base of glove box, near sub woofer / speaker there.
Sorry that’s about all I can do.
There are other members who have done this, maybe search for aux battery or voltage regulator and capacitor to help you locate those entries and possible photos.
Good luck.

TheSpooky

@Michaelscai
I got the same message. I will post if I find a solution, you do the same, please.

TheSpooky

Is this the replacement part?
Thanks

wagga_ria

Wonder if the aux battery can be disable?
I hate the start stop feature, and is the first thing I turn off when I start my Merc.

TheSpooky

Here is a linking replacing the same in C300. Looks like a simple job. Someone noted in comments that they changed it in GLC300 following these instructions. I ordered the part from Amazon. Will update when I am done replacing it.Wish me luck.

Michaelscai

I have been driving with that warning message in for months and have not had any issues . Is it something I need to take care of right away?

it sucks there is this auxiliary battery no other company I know of have it in the car. Totally retarded and I doubt I will buy another Mercedes again. It’s stuff like this that makes used Benz not hold their resale values

CorAegean

We just recently replaced the main battery on our GLC300. Now the instrument panel is AGAIN showing the battery symbol with the message "stop vehicle, keep engine running." With this message on, you cannot scroll to the main menu to see odometer or anything else.

My question: IF the problem is the "auxiliary" or "voltage regulator" or "parking fault capacitor" so it is NOT a real battery, but an electronic component, would it be covered by an extended warranty like a full exclusionary warranty? Please reply if you know or have had experience with this. According to the FCP Euro video below, this component is USUALLY the issue.

Thanks,
Reid C

mikapen

I think almost ALL cars and trucks are using auxiliary batteries these days. Too many electronics to keep alive between starts.

Teckno

GLC has no auxiliary physical battery - it is a poorly used term by Mercedes that confuses everyone, including warranty companies.
It is a small plastic box with a capacitor in it that is connected to the electrical system and is charged by the car.
NEVER claim replacement under aux battery terminology- always quote and have Dealer in Service Dept use term Voltage regulator- saves endless phone calls, rejection and pain.
Most warranty or extended warranty excludes batteries - this regulator has no battery, just a capacitor.
This item has been replaced under various warranty conditions by a number of owners.
Place your new car battery in engine area on charge overnight. There is a real possibility battery was on the shelf for a while and is depleted. Car will not charge an AGM type battery to full status, you need an intelligent charger, set to AGM type to sort this - something like a Ctek 5.0amp charger.
Good luck

abacnus

The rescue card would show the location of this Aux battery of your GLC. You could find a QR code on the door of fuel filling cap. Scan it..

Teckno

In Australia Mercedes placed the wrong scan details on the QR Code.
Again it is not a battery………
It is located under carpet in front passenger footwell , up against bulkhead or firewall under dash.
Fully sealed plastic box, about the size of a 30 packet of cigarettes that has a capacitor inside it, not serviceable, a toss away item.

Teckno

Found an interesting site in the UK that gives a good explanation into Mercedes and the GLC, use of the term Auxiliary battery and the malfunction issues.

HTTPS://xenons4u.co.uk

https://xenons4u.co.uk/a2059053414-a2059052809-a2054400073-voltage-converter-auxiliary-battery.html

The original article was several pages, but this link explains the GLC option.

Hope it helps explain the confusion why some models in the vast Benz range have lead acid rechargeable ‘batteries’ and others like our GLC models have Voltage Capacitor / Converters, called Aux batteries.
Article includes part numbers at time of writing.
Enjoy.

Tommy79

Hello Everyone!

Just wanted to share my same experience with Auxiliary Battery Malfunction fault... GLC 2016 250D 4matic, left hand drive, 115 000 Km, 6 years old (just over a month of the extended warranty!) "Start/stop" feature stopped working even if the function turned on... not that it's the end of the world (normally I switch off... like a muscle reflex) I haven't found any other unusual behavior... I drove only 20km after the fault and replaced the unit on the second day. The original manufacturer is Hella, it is the same part number as MB's part number: A 205 905 28 09



Talking to the main Mercedes dealership spare part department and an independent spare part dealership (one of the biggest chain in the country) there is no replacement part (don't get confused to noname Chinese un-labeled parts), only original manufacturer part... the new part number is: A 205 905 34 14


and here is the fault:



The electrolyte leaked from the capacitors on the PCB which caused shorting... nice burn smell after opened the casing.... No needed to replace any fuse or clear any fault code (for me)

Good luck everyone!