Hi all,

Just wanted to share some information that i got to experience. I bought the car pretty recently, a month ago, maybe a little more. All good, no issues, no codes whatsoever. Love the car and the driving experience. But randomly was getting "active headlights inoperative" - usually in the mornings, when was cold overnight, after car wash, or after rain. Also (i didn't even know until later) the eco mode was not working properly - the light was on on the dash / button, but the car would not turn off the engine at red lights. Adaptive high beams were not working either, and even got couple times "auxiliary battery malfunction" message. Obviously researched all the possible problems related to each code, was actually considering testing the modules for the headlights, maybe even replacing them, since they're way cheaper than the headlights.
But, since i own another MB, and got to read plenty of other people' incidents when it was related to the battery - decided to give it a try and got it tested. Initially the guy said that it was at half charge, which was already odd, considering i drive it daily 30+ miles. Then he tested it to see how it will work under load - and it indeed failed the test. It was still the original battery - the car was made in 2015. After replacing it with another one (you can buy a non AGM battery, they're usually cheaper, and cheaper for a reason) all the issues disappeared and, as i said earlier, i found out that the car has auto start/stop at traffic lights And adaptive high beams work And the"active headlights inoperative" message never came up again

Something to keep in mind next time you'll start getting random gremlins or other issues - it might just be the battery getting old. I definitely solved quite of issues and got myself peace of mind for the next 5 years

Regards.

 

Question, did they do the battery test while it was connected with pos and neg wires or did they pull the connectors off to check the battery V?

 

He checked it while connected to the car. Same time he checked my alternator - he told me to turn on the lights, max AC and radio, just in case my alternator was not charging the battery

 

Where did you have it tested? Checking the OCV with the cables connected won't give good readings (especially after having driven it to the shop). Load testing in the car when connected to the circuits is just asking for problems. I hope you didn't go with a non-AGM as acid damage could be costly. Marv

 

Where - do you mean the shop? It was not at the dealer, as I don't want to waste money on nothing. It's a reputable shop in my city. And yes, I went with an AGM, since the original was exactly the same.

Now why, in your opinion, testing while connected to the car, is asking for trouble? I understand it's a complicated car and has plenty of things to fry, but I never had issues with this shop.

 

I retired from the Battery business after 26 years with the World's largest battery company. It is always better/safer to load test a battery out of the car or at least disconnected. With all the electronics in our cars, you are taking the risk of damaging electronics. That's why I make those recommendations. Marv

 

It might not cause you any trouble, or it might, not sure, but sometimes if another wiring is bad and you test the battery while connected, it might not give the proper reading. My friend's car battery test said it failed 1 out of 2 tests...went to AutoZone to get it replaced under warranty. The dude replaced it without any questions, but also said test it while it is not connected to the car. Cuz if a connection is bad elsewhere, that might be draining the battery's life and the battery itself might not be the issue.
I mean you issue could have been just the battery, I hope nothing major. But that's what I was told from the guy from AutoZone. I mean, it does make some sense to unplug it before testing it. But again, I have no additional knowledge in this field. Just sharing my experience and what I heard.

 

Are batteries covered under MB warranty? (CPO / extended)

 

No, they only have a two year warranty. Go elsewhere and get an AGM replacement battery (Autozone, Advance, Napa, Walmart, etc). Check the dealer price, but don't let them charge you for install. You'll save $$ by going elsewhere and they will have a much longer warranty. Marv

 

Thanks. Has anyone run a larger than normal battery in the trunk? Thinking about adding a small trunk in the back.

 

Many auto parts stores, such as Advance, will NOT install a battery in an M-B product - company policy. They will sell you one, but are not allowed to install it. Rationale is that they have had problems in the past with the M-B electronics.

 

I have similar issues with my 2015 CLS, however I never got a battery malfunction notice. I did however pull the OEM auxiliary battery out and it tested with zero cranking power.

I replaced it with a new one however it wasn’t an OEM battery, the start/Stop feature still doesn’t work.

Do you really think since it’s not an OEM product it would cause the feature not to work?

Thanks

 

Jambert,

(I guess we're neighbors won't be surprised if i drove by you couple times)

Replacing it with a non-OEM battery shouldn't create issues. Sometimes is the process on how you do it or something relating to that. Was the start/stop feature working before that? I noticed that the start/stop does not turn off the engine every time i come to a stop. There is more than just coming to a stop that impacts the eco mode.

Which battery did you replace - the front one (main one, driver side, right under the windshield) or the one in the trunk (auxiliary)? All my issues disappeared when i replaced the main battery.

Also side note, not sure if related to that, i had a blown fuse of the OBDII port... So sometimes it might happen, just like El Cid said, thus some stores won't replace the battery if they don't have a backup device for all the systems in the car.

Again, an aging battery can wake up all kinds of gremlins, and you might not find 2 similar cases. In your case, if possible, i'd recommend getting a scan for fault codes. not a generic scanner, but something that can pull MB factory codes. If you don't have anyone who could do that, you can PM me and i'll give you one of my electric' contact info



P.S.

El Cid,

The store i purchased the battery from did it without any issues. They said they know how to do it right. So far so good

 

Neighbors eh! Very cool!!

The start/stop feature hardly worked but then again I drive very short distances in Elk Grove. Not sure if the engine is really up to temp based on my driving habits.

And I replaced the auxiliary battery in the trunk. Same power from volts/amps.

Send me a message!

 

I'd verify the front battery as well. Obviously it's a completely different car, but on my SL500 the smaller battery was for starting the engine only, and the bigger one was for all the other systems of the car. Considering our cars are about same age, i won't be surprised that your front battery needs replacement.

I also agree that the car might just not get enough energy recovered during short trips. From what i know, the car needs to run for at least 20-30 mins or 5+ miles to refill the energy used for starting the engine. If you drive daily shorter distances than that - i tend to believe that your main battery doesn't get enough juice, thus doesn't have enough power to run all the systems when ECO mode is on. I'm not a specialist on it and the ECO mode is still new among car makers, but it might be more sensitive than we think.

 

The front battery is the main starting battery, the small one is only used to balance the system voltage. The smaller Auxillary battery is found in different places based on the year of your CLS550. Under the driver side dash in 12-13 models and in the trunk for later models. Someone can correct me about the locations if I'm wrong. Marv

 

Nobody can beat Walmart prices lol I compared prices of Auto Zone vs Walmart... sometimes $100+ difference...same voltage/warranty
@Ghostty You guys aren't that far haha. I'm in Hayward.

 

Hello,

My CLS is a 2015, just replaced both auxiliary and main batteries.

-My Eco mode works again (stop/start)
-Assist park
-Not sure if it’s my imagination but my HK Logic sounds better.

My warranty unfortunately does not cover batteries so I was out about $450 for both installed including the relearn... but I’m hoping my batteries are good for the 3+ years 🙄

 

You went to the dealer?

 

No. brought my car to a local shop who specialized in European cars.

 

You mentioned "the relearn", what does that entail?

 

He means the process when you have to reset windows, radio presets and other stuff. If you don't use a backup device when disconnecting the battery, several systems' settings will reset to default. Not unusual but pretty annoying for sure...

 

Just changed the batteries. For the back just a 10mm wrench, and go with OEM part, FCP has it for like 138. I went with a Duralast Platinum which took a bit more work than the oem and costs almost the same (for 200CCA). Here is a write-up and video: http://tunedmercedes.com/electronics...liary-battery/

The front is basically just an H8 Battery (not exactly but an H8 works and should provide a bit more than 10% increase in capacity) and it slots in well. You need a 10mm with extension for this one. Here is a write-up and video: http://tunedmercedes.com/electronics...-benz-battery/

Replacing the front battery made my brake feel change back to how it was when I first got it. Firmer, sportier.

Replacing the AUX battery made the car seem faster, more decisive. The transmission started to relearn. Both of my batteries were 7 year old original MB batteries with 26k miles. It also made the car shut off at lights more.

 

Lovely write up, I'm about to do this.

I looked at fcp euro doesn't seem to have the aux battery, do you have a link to it? Oem.

 

thanks!

This should be the part if your battery is in the trunk (2012-2013? Are under dash and use a smaller battery).

https://www.fcpeuro.com/products/mercedes-battery-ml350-ml63-amg-ml550-mer-0009829308