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FYI: If you have the EQS parked for a long time, then it will automatically recharge the 12V battery from the high-voltage battery, whenever the 12V battery's charge drops. (I have done this several times now in the 1.5 years that I've had my 2023 EQS SUV.) There should be no need to hook up the 12V battery to a charger.
FYI: If you have the EQS parked for a long time, then it will automatically recharge the 12V battery from the high-voltage battery, whenever the 12V battery's charge drops. (I have done this several times now in the 1.5 years that I've had my 2023 EQS SUV.) There should be no need to hook up the 12V battery to a charger.
The HVB will recharge 12V only when vehicle is in operating mode (key position 1 or 2) or when connected on the charging port. Mine was in storage for 5 months and I was able to monitor dropping voltage from the distance with Mercedes Me.
No automated 12V charging did happen. May be they improved the SW for 23, mine is 22?
FYI: If you have the EQS parked for a long time, then it will automatically recharge the 12V battery from the high-voltage battery, whenever the 12V battery's charge drops. (I have done this several times now in the 1.5 years that I've had my 2023 EQS SUV.) There should be no need to hook up the 12V battery to a charger.
The HVB only charge the 12V battery when the car is on. During it sleep the 12V will continue to drain. If you let the 12v battery drain too much upon starting the car all you dash lights will lid up and you will have to reset thing the window express up/down. This happened to my car during a front end ppf install over the weekend. I couldn't get the sunroof to close properly so had to take it into the dealership.
My brother went out of the country the same time with us, he left his brand new MDX sat for 2 months, battery was dead when he got back, he checks the voltage and it is showing 2.7V, Dealership replaced the battery under warranty.
There also a worry in the back of my mind that leaving the L1/L2 plugged in will caused something to happen like a fire. I even though about parking the EV outside. Better be safe than sorry, i guess. LOL
However, a few other people have reported not seeing their 12V battery getting recharged automatically from the high-voltage battery, so YMMV...
IT is clear now that All EQS do not operate the same way. I am positive that my EQS sedan 2022 Edition 1 with SW 330.xxx does not recharge 12V battery automatically when in storage locked and no HVB charger connected. The MB me connect show 3 declining charge conditions over time. From fully charged, to acceptable charge and 4 months later LOW battery.
So for a model that function the way mine operate my recommendation are still valid.
Fantastic. This is significant news confirmation for all EQ owners who store their cars for long period of time. The same experience may not be true for other EV brands.
I wanted to store my 2022 EQS for up to four months when I'm traveling but got the dreaded "12v battery critically low" warning after two months.
I inquired at the dealer today, and they confirmed that the high voltage (HV) battery does not shunt over any electricity to the 12v battery unless the car is charging or being driven.
This seems to be contrary to some owners' experiences and I think I know why:
Although there has been copious discussion about the battery's state of charge, most are referring to the HV battery's state of charge, which should be around 50% for long term storage. No mention is being made of the 12v battery's state of charge prior to storage. This one should be as close to fully charged as possible for battery charge longevity since it is used regularly for vehicle telematic functions, even when the car sits idle.
So, the low charge warning for the 12v battery after months of storage is not a function of whether or not energy is diverted from the HV battery (it isn't), or even the HV battery's state of charge. It is dependent upon the state of charge of the 12v battery prior to storage. So the next time I leave my car for an extended amount of time, I'll either drive the car around or use a slooooooow level 2 charger so that the 12v battery will have sufficient time to fully charge. Once I get a "battery charged" indication on my app (for the 12v battery, not the HV battery), then I'll know it's OK to store my car.
And then hope that I'm right. I'll report back later this year.
Safe and happy motoring!
I think thus needs to indicate \"fully charged" before my car is stored to delay getting the "critically low" battery warning.
Last edited by haYnBenz; Jan 21, 2025 at 10:33 PM.
Reason: Added images
HayNBenz: This has not been my experience. I leave my car in storage in my winter home garage for at least 5 months over the course of the summer. I leave the HV battery in the range of 50-80 %. During the course of the summer the 12 v battery drops to partially charged multiple times. After a day or so it reports back as charged. I have discussed this matter with my service advisor both in RI where I bought the car and in Florida where I keep it. Both say when in storage for a long time the car goes into bulk mode and charges the 12 v battery. RI advisor even printed out a bulletin from Mercedes detailing how the car charges the 12v battery from the HV battery when in prolonged storage.
Thank you Radman991! If there is any way to get ahold of that MB bulletin, that would be so helpful so I can enlighten my service advisor and his team. I'll ask him about "bulk mode" and maybe that will help.
You'd think there be a way for my car work the same as yours.
HayNBenz: This has not been my experience. I leave my car in storage in my winter home garage for at least 5 months over the course of the summer. I leave the HV battery in the range of 50-80 %. During the course of the summer the 12 v battery drops to partially charged multiple times. After a day or so it reports back as charged.
I - and may other people - have found the same thing: The 12V battery is, indeed, frequently recharged by the HV battery when my EQS (a 2023 EQS 580 SUV, FWIW) is parked for several months. (Each time, I have left the car with an initial HV battery charge level of between 30-50%, as recommended in the driver's manual).
But a few other people have had your experience, and have found their 12V battery depleted after parking the car for several months. It would be nice to get clarity on why this is happening to them.
Last edited by finlayson; Jan 22, 2025 at 03:33 AM.
2025 Maserati Grecale Folgore and 2024 Jaguar F-PACE SVR
There's no alternator and regen is high voltage too so I don't understand how the 12V could NOT be getting recharged by the battery management system. At some state of charge it stops doing that though so the HV battery doesn't become fully depleted, which incidentally voids your eight year warranty after something like 21 days (don't remember exactly but it's in the warranty booklet that came with your EQS).
Thank you Radman991! If there is any way to get ahold of that MB bulletin, that would be so helpful so I can enlighten my service advisor and his team. I'll ask him about "bulk mode" and maybe that will help.
You'd think there be a way for my car work the same as yours.
Thanks again!
Its been so long since he gave me the printout and since the 12 v battery has always recharged I’m pretty sure I tossed the memo in the trash. I’m currently in Florida for the winter and it may be in my summer home in RI. Sorry about that.
In 2024 I stored my 2023 EQE SUV for about five months using a trickle charger on the 12v battery. The HV battery lost only about 2% during this time. Car behaved normally after I picked it up.
Fast forward to this year, 2025, where I also stored my car for about five months using a trickle charger for the 12v battery. (HV battery also lost about 2% during this time). Car has been behaving normally since I picked it up a week ago with one exception.
The exception is that I have, in the week since I picked the car up, only seen in MMe the 12v battery status as "partially charged" (and battery health "good"). I have always watched the 12v battery status obsessively since not long after I took delivery of the car in 2023 and more than half the time it would show "fully charged" -- and especially after HV battery charging. In last week's drive of 1900 km and many HV battery charges, I have not yet seen the 12v battery show "fully charged". Yesterday, with the status as "partially charged", I checked the service menu and it said the 12v battery was at 13.05 volts, which was a relief.
Also interesting is that in May of this year, just before I put the car in storage, it downloaded and successfully installed an update entitled: "Software Update for Vehicle Charging System: Occupant Restraint" The sub-explanation is nearly incomprehensible (at least to me). It says
"Mercedes-Benz upgrades the operating system to optimize operations and enhance your charging experience. This update offers an extension to your vehicle charging system to enhance charging functionality during an OTA update for your vehicle."
When I arrived home, I let the car sit over night with the charge level at less than 20% thinking maybe that would change this behavior. It did not.
Anyone have any similar observations or thoughts why I never to see "fully charged" any more? Could this be an early sign of 12v battery failure, despite the battery health still showing as "good"?
In 2024 I stored my 2023 EQE SUV for about five months using a trickle charger on the 12v battery. The HV battery lost only about 2% during this time. Car behaved normally after I picked it up.
Fast forward to this year, 2025, where I also stored my car for about five months using a trickle charger for the 12v battery. (HV battery also lost about 2% during this time). Car has been behaving normally since I picked it up a week ago with one exception.
The exception is that I have, in the week since I picked the car up, only seen in MMe the 12v battery status as "partially charged" (and battery health "good"). I have always watched the 12v battery status obsessively since not long after I took delivery of the car in 2023 and more than half the time it would show "fully charged" -- and especially after HV battery charging. In last week's drive of 1900 km and many HV battery charges, I have not yet seen the 12v battery show "fully charged". Yesterday, with the status as "partially charged", I checked the service menu and it said the 12v battery was at 13.05 volts, which was a relief.
Also interesting is that in May of this year, just before I put the car in storage, it downloaded and successfully installed an update entitled: "Software Update for Vehicle Charging System: Occupant Restraint" The sub-explanation is nearly incomprehensible (at least to me). It says
"Mercedes-Benz upgrades the operating system to optimize operations and enhance your charging experience. This update offers an extension to your vehicle charging system to enhance charging functionality during an OTA update for your vehicle."
When I arrived home, I let the car sit over night with the charge level at less than 20% thinking maybe that would change this behavior. It did not.
Anyone have any similar observations or thoughts why I never to see "fully charged" any more? Could this be an early sign of 12v battery failure, despite the battery health still showing as "good"?
I had a similar issue. The car was unable to install the last OTA update due to battery not fully charged. I tried driving car for 1 hour and also charging the HV battery overnight. Nothing successful and battery remained partially charged. Brought the car into dealership and they found the 12v was starting to fail. They replaced it and kept my car in lot overnight and the OTA was successful.
I had a similar issue. The car was unable to install the last OTA update due to battery not fully charged. I tried driving car for 1 hour and also charging the HV battery overnight. Nothing successful and battery remained partially charged. Brought the car into dealership and they found the 12v was starting to fail. They replaced it and kept my car in lot overnight and the OTA was successful.
Thanks. Do you remember what MMe indicated as the "Battery Health" while this was going on?
Obviously your battery health was not good -- but I'm wondering if we are faced with an app/monitoring system that cannot be relied on (i.e. it says the health is "good" when it actually is not.
Thanks. Do you remember what MMe indicated as the "Battery Health" while this was going on?
Obviously your battery health was not good -- but I'm wondering if we are faced with an app/monitoring system that cannot be relied on (i.e. it says the health is "good" when it actually is not.
battery health showed as good and partially charged.
Even after all the responses in this long thread, I haven't seen whether people are keeping their car doors locked or unlocked during long-term storage. Does it matter?
Even after all the responses in this long thread, I haven't seen whether people are keeping their car doors locked or unlocked during long-term storage. Does it matter?
During both my long-term storage events, the facility was a valet-type operation, so they may have locked and unlocked the car to move it, clean it, etc. I don't know. And in both cases, the garage was sufficiently underground that the car had no cellular signal, so i could not check status via my Mercedes Me app.
But, anyway, you pose an interesting question. Since the car does not lock itself, I presume under such circumstances the alarm will not arm...and thus there should be some reduced 12v power consumption.
Hopefully somebody else on here will know the complete answer.
The interesting thing is that for my old GLS580, the manual said Mercedes’ electronics enter a deeper “sleep” mode only after the car is locked. If left unlocked, the vehicle stays in a semi-awake state — interior sensors, communication modules, and key detection systems can remain active, leading to noticeably higher battery drain.
The interesting thing is that for my old GLS580, the manual said Mercedes’ electronics enter a deeper “sleep” mode only after the car is locked. If left unlocked, the vehicle stays in a semi-awake state — interior sensors, communication modules, and key detection systems can remain active, leading to noticeably higher battery drain.
I always double-press the lock button to turn off the SmartKey function. You have to do this to both keys. My spare key, which sits in a drawer nearby the garage, was double-pressed prior to putting it in the drawer so that it doesn't communicate with the car while it just sits there.
One way to doublecheck if you disabled the SmartKey function is simply by having the key in your pocket and attempting to unlock the car via the door handles. The door handles won't respond if the SmartKey function was properly disabled. The only way to unlock the car is to hit the unlock button on the remote. The vehicle will revert back to the SmartKey function once you press the unlock button.
I do the same thing whenever I park overnight on the road outside of my home to ensure there won't be any relay attack, although I haven't read anything about Mercedes having such an issue in the US (or anywhere really).
Wasn't there a software update related to the 12V battery a while back? I seem to recall it had something to do with charging the 12V battery. This might explain the different information being reported.
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