pandas

Hello All! My first post here, so please pardon my ignorance and thank you for your help in advance!

I have a 2013 C300 Luxury trim, and my Eco Start/Stop stopped working a few months ago. Today when I took the car for routine maintenance, I asked them to look for a cause. They told me that I needed to replace the Auxiliary Battery and want to charge me a whopping $550 for it, in addition to the $80 they charged me to diagnose the problem.

I looked online and came across part number 2115410001, which looks like it might be the aux battery for my model. Can someone please confirm if this is correct? Also, where is the battery located? Under the passenger mat or in the trunk? Any instructions on how to replace it?

Thanks very much!

tripper80

exactly the same issue. very rare resources online, not even sure if there is an auxiliary battery on 2013 c300 model (mine is 3.5L 4 matic model).

pandas

Thanks Tripper80! Agreed that the online resources are so confusing. That's why I thought I'd plead for help from the gurus here.

From my reading, it appears that the 2013 and 2014 models had a different set-up compared to the older W204 models, as Eco Start/Stop was introduced in the 2013 model. The 2015 model and up have some sort of a capacitor under the passenger foot well. I pried open my passenger carpet, but could not locate any auxiliary battery (unless I looked in the wrong place). There's a black box on the passenger side of the trunk where the spare tire is, which might be another possible location, but I'm having a hard time opening that plastic enclosure, as it does not have any screws, nuts, or anything. Hopefully, someone else who's been through this can help this newbie

tripper80

If my memory serves me right, one post I saw told me that there's no auxiliary battery for the 2013 W204 with 3.5L (M276 engine). If so, I would direct my work to other possible reasons. first, I'm soon to replace my alternator which gives a poor output voltage fluctuating from 11+V to 14.9V, plus my new battery has never been fully charged in three months with pretty much highway. other possible suspects include bad O2 sensor, bad MAF etc. Let's see how it works out and will keep you posted.

pcy

That black box you mention in the trunk houses the AUX battery. Remove plastic pins holding the cover of that plastic box. You will see heavy gauge wires. Look closely, inside all that fancy wires and electric parts, you will see the battery.


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pandas

Thanks so much, PCY! This is very very helpful! I peered slightly inside the box and it matches perfectly with your pictures.

I tried to pull out the plastic pins you mentioned by prying them with a flat head screw driver and using pliers. Is there a special tool to extract them? Afraid of breaking them. Any pointers would be much appreciated!

pcy

I use this tool (below). Nothing special about it. All auto parts stores sell tool like that. Harbor Freight sells them as well.
You just have to pull the center pin out.

pandas

Thanks very much! Will make a quick trip to autozone this afternoon.

pandas

I feel soooo stupid! I was trying to pry open the pin housing and not the center pin! So easy to do once you pointed out that I just needed to pull out the center pin.

Success!




2013 C300 auxiliary battery



550 bucks to do this????? In addition to the 80 they already charged me?? Insane! No wonder dealers get a bad rap!

Tom in Austin

Batteries Plus may be a good source for a replacement since they carry some unusual sizes/types of batteries.

BTW, the function of this battery is to run the car's electronics, e.g. radio, fan, etc. while the engine is off in 'ECO' mode. The system knows if the battery is low or out of power and prevents ECO mode from invoking under that condition.

JettaRed

iTrader: (1)

FCP Euro has the battery for $129.

https://www.fcpeuro.com/products/mer...300-2115410001

PolarWhite2014

My Start/stop quit a while back also. Just swapped out a dead main battery. Thinking my aux battery needs replaced also. 6.5 years for a battery is pretty good IMO. Looks like my O'Reilly store may have one for 107.00
https://www.oreillyauto.com/detail/b...enz/c300?pos=5

Tom in Austin

I'd say 6.5 years in a hot climate is pretty darn good performance. Where I live batteries burn up in 3 years or so ... though I don't drive the Mercedes as many miles as my other cars, so miles must go into the equation too ...

JettaRed

iTrader: (1)

There are certain operating conditions (such as coolant temp, charging system functioning, etc.) that must be met for the start/stop to work. I have a 2014 C350 Sport that I bought used and the start/stop did not work. It had a blown cigarette lighter fuse. Once I replaced that, the start/stop feature worked.

Make sure your fuses are all good and that the alternator is functioning properly. You can get a cheap tester to check the alternator. The tester showed I had a bad alternator until I replaced the blown fuse. After replacing the fuse, the tester showed a normally functioning alternator.

capt_paul

I have an auxiliary battery located in the trunk next to the spare tire. You have to remove the plastic button retainers around the case and then lift up the cover and you will see the battery

kenju4u

Hey All,

I am resurrecting an old thread but I suspect my Aux battery is going bad because my ECO stop / start never goes into "green" eco mode mode. There are no errors but eco on the instrument cluster stays yellow no matter what. Hasn't been working since at least 6 months with wide variety of driving conditions.

I tested the aux battery voltage and its 13+ volt. the main battery was 12.10V. It is 28 degrees outside. I still suspect the aux battery might not just be able to hold CCA capacity.

Is there anything else I need to test before I try and replacing the aux battery?

Ken

Odd Piggy

Replacing the aux battery solved the non functional ECO start/stop on our GLK350 without doing any other diagnostics. However, a weak main battety can also cause ECO to stop working. A heavy load test is necessary to determine if the main battery is getting weak. 12.1 V sounds about right at 28 F but a load test with a professional instrument can verify it’s capacity.

Tom in Austin

Yes, strength of the main battery is a factor in auto-stop. I had my C350 main battery out for a 24-hour charge and that restored auto-stop for a month or so. The restart was noticeably quieter and smoother too.

I think it must be characteristic of AGM batteries that they lose the strength to support auto-stop as they age.

kenju4u

Thanks I have a battery tester coming in from Amazon which should be able to help me diagnose this better. Through my OBDII i was able to confirm the battery is being charged while the car is running at 13+ volts and no errors.

Ken

Gazwould

Why on earth are these people thinking Stop Strain is a good thing.

Odd Piggy

Excuse my ignorance but are “Stop Strain” and “ECO Stop/Start” the same thing?

kenju4u

Its been proven that stop start does not damage the engine. It does save gas though.

alecmascot

Odd Piggy

Our friend from down under was a bit rough on the colonists. He was rougher on the stop/start systems, though. My wife has been pushing the button to shut the thing down before getting out of the driveway since 2014 based on how much of a PITA it is at stop signs. Looks like she got it right!

Then there is the discussion over why this thing is in the car in the first place….

Gazwould