My C63S is only used a couple of times a week and sometimes it can be in the garage, unused, for a couple of weeks. I'm very familiar with the "Starter Battery" warnings that occur through lack of use, and possibly due to the car being nearly 7 years old and still using the original battery. I resolve this by performing a slow charge, then it's okay for a while.

Yesterday, I got a new warning relating to the "12V Battery", so not the Starter Battery. I'm fairly sure I haven't seen this message before. It's currently on charge. I'm now thinking it is time to replace the battery, although it's due a major service next month, but I know they will charge a fortune for what is a fairly simple task that I've done on other cars before, the most recent being my Jaguar XKR.

What I'm not sure about is how many batteries this car has, given that it refers to Starter Battery and 12V battery.

Googling suggests there is one 12V battery under the bonnet (hood for those in the US) on the passenger side, and this is where I connect the charger's positive connector. There also seems to be an auxiliary device fitted in the footwell and rather tricky to get to, but I don't believe this is a battery, just an electronic device.

I therefore have a number of questions that I really hope you can help me with:

1. Why the different warning messages referring to Starter Battery and 12V battery? Clearly, recharging the "main" battery resolves the "Starter Battery" warnings, so why the distinction?
2. Which replacement battery would you recommend for a 2019 C63S?
3. Is it really necessary for codes to be reset after replacing the battery? Googling indicates many people who have changed batteries without having codes reset and without any issues? I did wonder if I could ask for the codes to be reset during the service next month, but they may refuse to do this on the grounds they didn't provider or install the replacement battery.

Thanks in advance.

 

Starter battery and 12V battery is used interchangeably. They've been changing the terminology, because of the confusion when it comes to EVs. Yes, after 7 years, your Starter Battery/12V battery is probably done. AGM batteries typically last 4-6 years. I got mine replaced last year. I had it done at the dealership. Cost me about $500. As for the module under the passenger side glove compartment, that's commonly referred to as the aux battery. In some models it's an actual battery, but in our case it's a capacitor module. It's recommended to replace it at the same time, although it has its own warning message in the instrument cluster if it needs to be replaced. My dealership didn't replace it, so I went ahead and replaced it myself. The part was about $120 on FCP Euro and yes you have to remove the carpet and the paneling to get to it, but it isn't all that bad. Doing it the first time took much longer than it was supposed to as I didn't wanna break anything while figuring out how hard to pull on the panels to release the clips. Here's a YouTube video that I followed.


As for programing the new battery some say it's a myth other say it's necessary to make sure the computer knows it's a new battery and charges it accordingly. There are several folks on here who have replaced the battery themselves w/o any coding and haven't had any issues. It's up to you. I could have replaced the battery myself if I wanted to, but dealership had a special and for $500 I just had them do it.

 

Thanks for the info superswiss, it is very useful.
I assume if the dealer installed your replacement battery they would have used an OEM battery?
I'm going to call my Merc dealer tomorrow to book a service and will discuss the cost of installing a new battery and auxiliary capacitor.
I may also speak to the parts department and compare prices to those I've seen online.

 

Yes OEM battery

 

DieHard

@superswiss

500$ from MB ?

OEM Battery is as i know from Varta .

My battery is also on End.
For winter i need a new.

 

Yes.

 

After 3 1/2 years my battery on me commect app would always show Partial Charge. 2019 C63s coupe.



Then an in dash warning appeared see photo below (lower picture) I called the dealership and said to bring it in instead of driving for extended period to re charge it.

So I drove over and the battery was not OK. They replaced it while I waited.. It was still under warranty. See invoice below on what was done.

 

The battery in my 18' C63S is in the trunk. I believe it's an H8 size (haven't looked for a while) and Costco sells those (and the H7 size, if it's smaller) for about $190. (Interstate brand). Swapping it out should be able to be done with simple had tools... No need to spend $500 for that. However "registering" the new battery, if required by the computers in our cars, would require Xentry, and I haven't looked for that service function yet. I also can't find a manual process for resetting / registering a new battery for a Mercedes. A quick internet search for how to do it in Xentry says this: "Access the Signal Acquisition Module (SAM) using the diagnostic tool, navigate to "actuation tests," and select "confirmation battery change" to reset the charge count to zero."

Because I only drive my MB about once a week, I leave it on a Noco Genius 5 100% of the time it's parked in my garage. I always use the charging posts in the engine compartment and never use the battery terminals themselves for charging (more on this below).

​​​​​I have no idea if this applies at all to Mercedes vehicles, but I do have experience with battery maintenance and charging with newer Ford vehicles. The newer Ford cars all have a BMS system (Battery Management System) that uses a small device mounted on top of the negative battery terminal to monitor the voltage, and the rate of discharge and rate of charge. There is also a setting (coding) in newer Ford vehicles for the SOC (State of Charge) and it is factory set at only 80%, supposedly for battery longevity. So these systems tell the vehicle to charge the battery only to 80% while driving (no matter the time-length of the drive). The charge is computer controlled by regulating the output from the alternator and it is well documented that it is a tapered / sloped down charge rate as it approaches the SOC setting. So if your battery was at 70% for example, and you only drove 10-15 minutes it might have only charged to 75% because the charging rate is slowed down as you approach the SOC setting of 80%. This is problematic for people who frequently take short drives because the battery never gets charged back up and can sit in the 60% capacity area quite a bit due to the drain of all the systems that remain powered even while the car is off (remote start monitoring, over the air updates, proximity monitoring for touch door lock systems, etc.). The point is that when you just slap a new battery in and you don't reset the BMS the vehicle uses the old data from the rate of discharge and rate of charge and SOC to regulate the alternator, therefore you may never get full use of your brand new battery's capacity because the vehicle thinks it's still the old one. The process for Ford is to ensure the new battery is charged to 100% and then reset the BMS system. There is either a manual process that can be performed, or a computerized process that can be performed to reset the BMS. Either one works. The fix for a lot of Ford owners is to use ForScan software to change the SOC setting to 90 or 95% so the alternator charges the battery more aggressively, especially on short trips.

Another matter is that on newer Ford vehicles you must charge the battery by connecting the charger to the positive battery terminal, and the negative side ONLY to chassis ground point, or the top of the BMS sensor itself. If you connect a charger to the negative battery terminal the charge input bypasses the BMS sensor (that sits atop the negative terminal) and throws off the learned tables the computer had about SOC and charge rates. This is why I mentioned above about always using the charging / jump starting posts in the engine compartment for the Mercedes, so that any charging from my Noco Genius 5 goes through whatever systems are on the Mercedes for battery monitoring / management.

Hope this helps.

 

Hi Roysup, on my 2019 C63S the 12V battery is under the bonnet (hood), where there is a negative connection point on the engine block, that I always use when charging. The negative battery terminal can't actually be accessed under without removing the plastic covering.

Thanks for the info regarding BMS. This is similar to what I have Googled elsewhere, so good to know.

While I understand it is preferable to have the BMS reset whenever a new battery is installed, it does make me wonder if the system can "learn" from the battery. What I mean by this is that when the car is new and it has a new battery, the battery will be much more efficient, but over time as the battery ages, it will start to "fail" and I would assume during this decline, the BMS will monitor it, potentially charging an older battery more than it would a new battery. So, if the BMS system can "monitor" the battery and adjust the charging process to accommodate the age of the battery, why doesn't this happen the other way around? If a new battery replaces an old battery, initially the BMS doesn't know it is new (assuming it hasn't been registered). So, does BMS "learn" about the new battery over time and adjust the way it is charged, or does it simply continue to treat it as an old battery and continue to potentially over charge it?

I've not come across anyone saying their battery has been ruined as a result of not registering it as new.

I can see a large number of OBD2 scanners for sale on Amazon UK and other places. Not sure if they will allow a battery to be re-registered and I've never owned or used one of these scanners, but may look into them out of curiosity.

Although my battery spent a full day on a slow charge yesterday, the Mercedes app is showing it as "Partially charged", which is better than a warning that it needs charging, but not ideal and does suggest it is passed its best.

 

H7 ( coupe - others i think too but dont know for sure)

Varta DYNAMIC AGM 580901080 / 80Ah

 

@milleniumaire Your thought process is exactly why many people have reported no problems at all by just swapping the battery. The the same issue is common with Jaguar (OEM software is harder to find). But any BMS in the car "should" learn the new charging strategy for a new battery installed. But the "preferred / correct" way is to start fresh with a "battery reset".

You might check out iCarSoft products. The "CR Elite" one I linked says under "8 Hot Service Functions" that one of them is: "Battery Management Service".

The MB specific iCarSoft product HERE didn't specifically list a "Battery Management Service", only a "Battery Test", so if you get that one I would inquire with them if you can "register a new battery" with that device like Xentry would.... "Access the Signal Acquisition Module (SAM) using the diagnostic tool, navigate to "actuation tests," and select "confirmation battery change" to reset the charge count to zero."

 

Although my battery spent a full day on a slow charge yesterday, the Mercedes app is showing it as "Partially charged", which is better than a warning that it needs charging, but not ideal and does suggest it is passed its best.

At the end of my battery life once while was car was at the dealership and the doors or something else were left open. My me mercedes showed the battery was in Critical mode. The dealership said no problem the car just needed to be run for a while. Soon after the car was at a car spa for 3 hours or so with doors opened. Soon after, the battery then showed Critical mode. Then the on dash revealed Check 12 v battery. Check Owners manual. As previous stated when to dealership and battery was changed.

 

Although my battery spent a full day on a slow charge yesterday, the Mercedes app is showing it as "Partially charged", which is better than a warning that it needs charging, but not ideal and does suggest it is passed its best.

At the end of my battery life once while was car was at the dealership and the doors or something else were left open. My me mercedes showed the battery was in Critical mode. The dealership said no problem the car just needed to be run for a while. Soon after the car was at a car spa for 3 hours or so with doors opened. Soon after, the battery then showed Critical mode. Then the on dash revealed Check 12 v battery. Check Owners manual. As previous stated when to dealership and battery was changed.

 

@jj18 What amperage is your "slow charger"? If it's only a 1 amp like many of the old-school battery tender's were, then you might have to leave it on there for days to get a full charge.
I'd recommend a 5 amp or 10 amp "slow charger" like the Noco Genius 5 or the Genius 10. Either of those should get the job done in 24 hours or less, plus they have some reconditioning features and cycles.

 

Paper thats luxury for US citizen.

I have only pdf in FL .

 

Yes. My 1st paragraph was from the previous post and not mine. My mistake on how I posted it. After the first paragraph is what developed on my battery situation.

 

Something else I forgot to post. A good way of judging the state of the battery is to check the standby mode and see how many days it says that it can go w/o a charge. And activating the standby mode if the car is left parked for an extended period is what this is for. This is only available in the FL, partly because of the expanded online services. The cellular connection is also on when the car is parked, so like with your smartphone, that will slowly drain the battery. Activating standby mode turns off the online services and the cellular connection, equivalent to fully powering down your smartphone. It also turns off the alarm, as that is another battery drain, so only use the standby mode if the car is parked securely in a private garage. With the battery fully charged I get around 21 weeks, which is plenty, but since I replaced the battery I haven't seen the partially charged status in the Mercedes app anymore even after I haven't driven the car for a couple of weeks.

 

My Ring RCBT30 charger is a charger/starter and can deliver a 30A charge.