I dropped my car off at my tint/PPF guy yesterday and during the day I got a message from Mercedes Me saying the starter battery was critical. Today the car is completely dead.

The manual says Mercedes are the only ones who can charge the 12v battery, that can’t be right? Anyone know if you can just hook up a normal battery charger? The main battery had a state of about 50% when I dropped it off.

My tint guy also said that the lights at the charge port showed two red lines…

Interesting that all of these EV's seem to be having 12V issues. First Tesla, then both Audi and Porsche, and now the EQS. I know we had one report of a 12V dying a few months back but for some reason his car was fine after a few hours.

Is there a charge area under the hood? I remember reading for all the E-Tron and Taycan issues they'd have tech's open up the frunk to access it.

That is unfortunately a correct read of the owner's manual. One last ditch. Try plugging the car in for a bit. Let it charge then try turning the car on to the accessory setting then "start". You might be able to force the HV battery to recharge the 12V.

I wonder if you can "jump start (not really but you get the idea)" the 12V battery using a trickle charger but I am worried about safety issues due to the amount of high voltage electronics under that hood (another reason why MB doesn't encourage customers opening it) but I am curious nonetheless. That being said, don't do it for the sake of safety.

I am wondering, the electric vehicles also use AGM batteries right?

Here is the information on where the 12V batteries are located courtesy of forum member Diesel Benz: https://cimg4.ibsrv.net/gimg/www.mbw...bfecfac7ee.jpg

Here is another battery failure thread forum member js_cls was probably referring to:
https://mbworld.org/forums/eqs/83282...y-failure.html

As for opening the hood, once you open it make sure to not start touching things, this link was shared by another forum member here: https://tiremeetsroad.com/2021/12/19...-mercedes-eqs/

UPDATE: Spoken to multiple dealerships and the consistent message is that you should NOT "jump start" the car as it can lead to damage. It's currently plugged into the emergency 110V charger on suggestion from a service tech and a flatbed is on the way to take it to the dealer. I suppose this is the downside of buying a brand new generation of car, seem to be a lack of knowledge amongst the dealerships on how to handle failures.

I'll keep updating the thread once I know more as I hope this will help someone in the future.

Thanks for confirming and for your update.

I had followed the Taycan and Etron 12 volt battery travils, lurking on their chat boards, as I drove both and was considering purchasing both. Didn't know Tesla also had this issue. My question is, with all these marques having had the issue, and all the smart gearheads driving all these machines, has anyone figured out what we can do to prevent this from happening? I think with the Etron, it required a software update. Any other ideas?

I don't understand how this can happen if there is plenty of charge in the 108kwh battery pack. The 12V is charged from the 108kwh battery. There is no alternator here.

Unless your guys drained the big battery to the point that it shut down for preservation and this then led the 12v battery to die.

I can understand it, maybe, being left with doors open and interior lights, etc working at the tint shop, because that draws directly from the 12V battery. But many of the issues on other boards occurred while cars were being actively driven. I am at a loss to explain those issues. With Porsche/VW/Audi is was a software issue which did not provide charging current to the 12 v battery. But others have had the issue as well. It is very confusing and frustrating to me, to have a new EV disabled by a dead 12V battery.

UPDATE #2: Flatbed showed up and the guy DID hook up a battery charger to jump start it (since he was sent by Mercedes I guess it was OK) and sure enough, car started right up. A few things didn’t work such as windows wouldn’t go down/up, seats wouldn’t move but I was able to drive it. We took it on the flatbed to the dealership and they asked me to drive it for 20-30 minutes which I did and now it’s like it never happened.

FWIW, the main battery has about 50% charge so it was just the 12v that drained. I spoke to the service tech and apparently there’s a way to put the car in standby/sleep mode even with the doors open. Have to look through the menus/manual to find how to do this or else this will happen again as the tint isn’t done yet.

Interesting, so it sounds like the technology drained the 12V while in for tint?

The 12v battery terminals are on rear back end of the "engine" bay. In usual MB fashion, there is a red box with the positive and a metal stud a few inches away as a ground. The battery works like any normal 12V. You can trickle charge or "boost" it. As soon as there is connected 12V source the car will start. Easy.

Technically it’s very easy. From a warranty perspective I was warned by a Mercedes tech that if I do it myself I could potentially void warranty. While I don’t see how that could possibly be the case it did make me hesitate.

It is because the EQS has nothing user serviceable under the hood and the customer shouldn't be allowed to open the hood in the first place. They don't want you injuring yourself or others, plus if they really have to track you they can see your vehicle is connected to a charger away from the dealership via Mercedes Me and if there is no evidence or record that they sent a personnel to your place to open the hood at such location they can void the warranty.

​​​​​​​Absolute BS. A car you own is a car you own. No company can limit who services your car. It's black letter law. As long as you don't modify a vehicle beyond its specs, they have to honor the warranty.

I would agree but they specifically say the EQS hood shouldn't be opened by the customer. There is a high risk of electrocution if not careful.

In fact, there are no exposed high voltage components.Unless you start taking things apart, it's completely safe. Not only is it the only way to service a 12V battery, but it's also essential to clean up leaf clutter from climate filters. Finally, it's also where you add coolant if the level is low. Not everyone has a dealer in the neighborhood. My dealer is 90 miles away. Im I supposed to tow the car 90 miles for a simple dead battery or to add coolant? Very stupid....

Good to hear that MB took extra measures to cover various high voltage components just in case the customer actually open the hood and accidentally touch something. I do agree with you though, it is your own car you should have the right to service it yourself but I guess MB doesn't want to be liable with any injuries caused by mishandling so they discourage you to repair it yourself on their fully electric vehicles. The right to repair, ah what a beautiful thing to have.

Frigging lawyers.

I had this exact same situation happen. The day I dropped it off for PPF I started getting starter battery critical notifications. I called them right away to relay the message and had them turn the car on fully whenever they were working with doors open/lights on. The app continued to show critical status, but when I picked it up it powered up and engaged the drive system with no errors. I think if they had not turned the car on fully while working on it, I would have been in your position.

Interesting. I didn't have a problem when mine was tinted, but what I did do was reach up to the upper console and turn off the interior lights by clicking the right-hand button on the control console behind the rearview mirror. That may have saved me, as the interior lights, then, were not on. Maybe that is something we all should consider if someone is going to be working on the car. Still, a pretty crazy situation to be stuck in.

The easiest way is to connect the car to a charger when you are going to keep it open for hours. But yet Mercedes doesn't want you to open the hood....... hasn't anyone noticed that all cars on car shows are connected that way?