"The Facts Are In: You Shouldn't Worry About EV Battery Replacements"

https://insideevs.com/news/779210/ev-battery-replacements-data-tesla/

Any EV built 2022 and after is considered to have Gen 3 battery technology per battery research company Recurrent, with a failure rate of only .3%. A statement I particularly find encouraging was this:

"All told, Recurrent expects new EVs to not have any issues for 15 years at least."

 

I am in for the long-term for this car, 10+ years, so my two minor worries are:
- loss of capacity over the lifetime (reduced range especially in winter)
- the battery will outlast the car which will be obsolete at that time

 

I hear you. A wise friend of mine from Iowa buys his vehicles with the worst-case scenario firmly in mind — getting stuck on a secondary road during a blizzard, temperatures well below zero, and potentially being stranded for many hours before roads are passable or help arrives. In that scenario, I agree: I’d want to be in my 2024 F-150 with a nearly full tank of fuel.

That said, I’ve always been somewhat of a risk-taker, and I’ve largely moved past range anxiety through careful planning. At this point, we have two EVs as our daily drivers. About 95% of my wife’s driving is under 60 miles per day, and I drive an EV roughly 90% of the time when my daily usage is under 100 miles.

In the summer, when my driving occasionally stretches to 400–500 miles or into more rural parts of Colorado, that’s when I take the F-150. We also take the F-150 on ski trips, where under ideal conditions it offers up to 600 miles of range and provides an extra margin of confidence.

As nice as the King Ranch F-150 PowerBoost is, I’ll choose the EQS or EQE every chance I get — which ends up being about 90% of the time. I’m not interested in living in a PHEV middle ground just to cover the 10% of driving where an EV may not be ideal, especially when the benefits of a full EV like the EQS or EQE are realized the vast majority of the time.

So for us, the answer is simple: we’re a hybrid household by fleet, not by vehicle — roughly 10% ICE and 90% EV — and that balance works exceptionally well.

 

Well, my hi voltage battery was just replaced after 3 years in my EQS 580. I certainly don’t expect this new battery to fail anytime soon, as I may keep this car for several more years if no issues arise. I will say I’m also on my third 12 v battery. I store the car during the summer months and that may be part of the problem, especially with the 12 v battery. I’ve been away on holiday for a week and my 12 v battery has dropped to partially charged status. I’m hoping with the new hi voltage battery the 12 v will recharge itself to full status as designed.

 

Not sure you would be better off in the stuck in the F150 with a full tank vs an EQS with a heat pump with a full battery.

 

What were the signs of your high voltage battery failure?

 

We have something similar. EQS 580 sedan, Toyota Tundra 1794, and a Porsche 981. Which do you think we drive the least to the point of needing to put a battery tender on it?

Also, we are in DFW so no stuck in the blizzard here.

 

The car was in storage. Despite having a trickle charger on the 12 v battery as recommended by 2 separate service advisors, the battery completely discharged and would not accept a charge from a regular charger. The car would not function. I had to use the blade key to unlock the car. That’s as far as I got. Car was completely dead in the water. Called the dealer who said it had to be flat bedded to them. Took 1.5 hours to get it out of my garage on to the truck. Dealer said “no communication between the 2 batteries and after 2 months of trying this and trying that, and contacting Germany, was told hi voltage failure and needed replacement. Replaced both hi and 12 v batteries. dealer had the car for close to 10 weeks.
I just went away for holiday break with car left in my garage and after 7 days away the 12 v battery reads as partially charged. 3 days later and still says partially charged. I was told car would sense 12v was low and it would automatically recharge the 12 v battery. Hasn’t done it yet and I’ve only had the car for 2 weeks since the batteries were replaced . I hope I don t run into same issues again. 23 EQS 580 sedan

 

I hope everyone doesn't fault me too badly for describing what you've shared here regarding your 12V and HV battery experience with an AI - in this case ChaptGPT. Please take the following, for what it is worth only , as everyone knows these AI's can jump to erroneous conclusions so take all of the below with a grain of salt:

ChatGPT response is below this point:

Below is a measured, technical analysis of the situation, grounded in what Mercedes documents, what is known about EQS electrical architecture, and what is probable — without jumping to conclusions or implying owner error.



I’ll structure this in four parts:

1. What the facts clearly show
   
2. What is unlikely
   
3. What is very plausible
   
4. How I would respond to this owner, constructively and calmly
   

1. What the facts clearly show (no speculation)

From Radman991’s account, several things are unambiguous:

• The car was in extended storage
  
• The 12V battery fully discharged
  
• The car became totally nonfunctional
  
• Dealer reported “no communication between the two batteries”
  
• Mercedes corporate ultimately authorized HV battery replacement
  
• Both HV and 12V batteries were replaced
  
• After return, the 12V state-of-charge behavior still appears abnormal
  

Those facts alone tell us something important:



👉 This was not a simple 12V failure

👉 Something prevented normal HV→12V support and monitoring



Mercedes does not replace HV packs casually. The threshold for that decision is high.

2. What is unlikely

Several commonly suggested explanations are unlikely given the details:

❌ “Just a bad 12V battery”

Unlikely because:

• The dealer explicitly stated loss of communication between HV and LV systems
  
• The HV pack was ultimately replaced
  
• Mercedes engineering (Germany) was consulted
  

A bad 12V alone does not require:

• 10 weeks of diagnosis
  
• Engineering escalation
  
• HV battery replacement authorization
  

❌ “User misuse” or negligence

Also unlikely:

• The owner followed dealer advice
  
• Used a 12V trickle charger
  
• Is an experienced Mercedes owner
  
• The failure occurred during storage, not abuse or extreme use
  

Nothing in the description suggests reckless charging, deep cycling, or modification.

❌ “This proves EQS batteries are unreliable”

Also not supported:

• This is a single case
  
• Warranty covered the repair
  
• Fleet-level data still shows very low overall HV failure rates
  

This case is important — but not representative of the population.

3. What is very plausible (and consistent with known EQS behavior)

This is where the evidence points — without asserting certainty.

🧠 Key architectural reality

On the EQS:

• The 12V system is not just accessory power
  
• It is required for:
  • HV contactor closure
    
  • BMS communication
    
  • DC/DC converter operation
    
  • Module wake/sleep management
    
  • HV battery monitoring during storage
    

Mercedes explicitly states:


If the 12V battery is disconnected or deeply discharged, HV battery monitoring cannot occur

🔋 Very plausible sequence of events

A plausible chain, based on known EQS behavior:

1. Extended storage
   
2. Gradual 12V discharge
   • Even with a trickle charger, if:
     • the 12V battery was already weakened
       
     • the charger was insufficient for intermittent module wake cycles
       
3. 12V voltage dropped below a critical threshold
   
4. Control modules shut down
   
5. DC/DC converter never re-engaged
   
6. HV pack could no longer:
   • report state
     
   • close contactors
     
   • support the 12V system
     
7. Vehicle appeared “dead”
   
8. Prolonged low-voltage isolation likely caused:
   • HV pack protection flags
     
   • BMS fault states that could not be cleared
     
9. Mercedes engineering determined the pack could not be safely revalidated → replacement
   

This is not misuse, and not even necessarily preventable once the cascade began.

⚠️ The post-repair 12V behavior is important

The owner reports:

• 12V showing “partially charged”
  
• No obvious automatic recharge yet
  
• Only two weeks of ownership post-repair
  

That suggests one of three plausible things:

1. Normal EQS behavior
   
   The EQS does not continuously top off the 12V battery; it does so under specific conditions (awake states, HV SOC thresholds, sleep cycles). The app is not real-time.
   
2. The new 12V battery is still learning / calibrating
   
   Mercedes systems do track charge history and adaptation.
   
3. Residual control logic or software updates pending
   
   After major battery replacement, it is common for multiple software layers to be updated or re-synced.
   

At this point, this behavior alone does not indicate recurrence — but it does justify monitoring.

 

Thank you for that explanation. I can’t argue with what was stated. I have returned from my holiday escape and will be back to driving my car again. When I was having issues with my first 12 v battery, the service advisor said the car needs to be driven every day so that the batteries stay up to charge. That’s difficult for me as I have 2 houses and split the year between Florida (EQS) and RI.

 

That seems like a ridiculous viewpoint to adopt on the dealer's and MB's part.

For many years, I owned a 1931 Franklin. I think I drove it, perhaps, 3 times a year and its 6-volt battery managed to start it after sitting without any problem. Of course, there was a hand crank as back up ;-)
I am sure the magic was that there were most certainly no computers involved!

 

I wouldn't worry about EQS battery at all.

First it is warrantied for 10 years 150k miles.
I bet the major ticket item for this car will be the airmatic suspension, if not anything else.

Second, there are EQS groups on Facebook with owners who have passed 160k miles and have 97% battery life remaining. The CATL battery, although Chinese-made is No.1 in the world and have no big issues of fire risk or cell failures like bad Chinese batteries like Farasis.

Third, it is a bit irrelevant but seeing how W223 counterpart is aging that thing probably needs a major engine and transmission service around 100k miles, costing 10-15k. I see EQS batteries from junkyard or third party vendors (original MB battery though) for 15K to 20K and the prices will be way cheaper at the time when the battery warranty ends in 10 years. Also shops that can repair only the bad cells are becoming more common, which can save owners thousands in repairs.

Fourth, Most of you will be driving something else by the time the warranty ends on the battery. The used values are already at the bottom. How much can you lose when the thing mechanically totals itself? I plan to keep my EQS until my extended warranty runs out in 2030-ish... and switch back to gas S-Class when W224 comes out

 

At least in the beginning, it was well known that the EQ models do not keep the 12V battery charged while the car is parked. The thing is, in an EV the high voltage battery gets disconnected when the car is turned off. So all the high voltage circuits are deenergized. This is partially for safety when somebody needs to work on the car. In order for the high voltage battery to charge the 12V battery, it has to get connected and energize the high voltage side of the car while parked. That could be dangerous for anybody working on the car when it happens to take place suddenly. Therefore like with an ICE, the 12V battery was only charged when the car was turned on. At some point I've read that there was a software update to change this, so that the 12V battery gets charged even while the car is parked, but I never found any confirmation anywhere that this is really happening. 12V battery issues have been an ongoing problem with many EVs. As you've found, if the 12V battery is dead, you can't turn on an EV. This is because the 12V battery powers the circuitry and switches that connects the high voltage battery. So it's kind of a chicken and egg situation. If the 12V battery is dead, it can't power the electronics to connect the high voltage battery that could charge it back up.

Here's one thing you can try to shed some more light on this. Remotely turn on the climate control to cool/heat the cabin, and see if the 12V battery charges back up at the same time since this will connect the high voltage battery to run the climate control.

Unfortunately, this will deplete the high voltage battery. For long term storage, lithium batteries should be kept at 50% SoC. That's also MB's recommendation. In addition they recommend to unplug it and check the charge every 6 weeks. If it's at 30% or less, plug it in and charge back to 50%. What SoC do you keep it? I wonder if the 12V battery isn't charged when the SoC is at 50% or less as it senses long term storage.

 

Based on all the problem reports it is reasonable to conclude that the first models only charged when the car was turned on. A software update was the resolution and this was then standard in subsequent EQS models, and first gen EQE models. MB does not publish details on any of the software improvements unless it is part of a safety recall, so it is difficult to identify which update and was it via OTA.

 

When I first started experiencing discharging of the 12 v battery while in storage (over a year ago) the service man printed out a sheet from Mercedes describing how while in storage the car goes in to “block” mode (I may have the incorrect term ) and the hi voltage battery replenishes the 12 v battery. This actually did occur previously as I would watch the battery go down to partially charged and within 3 days would be fully charged. This past summer things changed significantly. Despite trying a trickle charger , the battery would not charge up. I may have put the charger on the battery too late, after it drained to the point it wouldn’t accept a charge. The hi voltage battery was at 65% SOC. I will try turning on the climate system and see what happens

 

How did it come about that you had a 1931 Franklin as a daily driver? My1st car, in 1971, was a 1956 Lincoln Premier, which I enjoyed thoroughly, however, I much prefer our EQS and EQE!

 

To be fair, in 1931 there was no keyless entry, always on cellular broadband that allowed remote control of the vehicle at any time and car alarms. All this requires computer modules to stay powered in a sort of connected standby mode where they are listening for incoming signals and then fully wake up if a command is received or an event is triggered. Modern cars are like most consumer electronic devices. They never fully turn off, unless you unplug them. So there is a constant power draw at all times. My house for example still uses 3.3-3.5 kWh per day even if nobody is at home and using smart plugs to fully power down most devices around the house when I go away for an extended period, but the fridge/freezer, my network gear and my security system remain powered in order to protect my home, keep what's in the fridge/freezer from spoiling, and so that I can remote control my smart devices at any time and my alarm system can send alerts and contact the central monitoring if there was a break-in. When at home, it uses around 9-10 kWh per day on average, so 1/3 is just base load.

Some MB models have a standby mode that can be activated for longer term storage. My AMG has it. This mode turns off most remaining modules that constantly draw power. Specifically it shuts down the alarm system and the online service/cellular connection, so essentially the only thing that stays awake are the door modules, so you can still unlock it, but even those eventually shut down if the 12V battery gets low and need to be woken up by pulling the door handle. This is another thing that doesn't work anymore on the newer MB models with the retractable door handles. The door modules have to remain powered, otherwise the door handle won't extend next time you are ready to drive the car. Lots of unnecessary tech in modern cars to be honest that don't really solve a problem, but create new ones.

 

You would be shocked at the number of people who die of carbon monoxide poisoning in trapped cars. The snow builds up behind the car, forcing exhaust gases under the car, which then rise into it. You're better off with no fuel and a blanket. Living in the Rockies, every autumn we would load the car with food, water, and blankets before driving in the mountains - you never knew when the first snowfall would arrive, so needed to carry supplies in case you became trapped.

 

Beautiful! No, the Franklin was not my daily driver. Just a vintage car I owned and did not use very much.