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Also, i noticed the charger gets really warm as well. At least initially, then it slightly cools off (but is still warm to the touch). Is that because of the different charging cycles or should i be concerned as well?
Mine is actually hot to the touch. It’s been that way since I got it. I does cool off as the charging process continues, then when it’s fully charged, it’s cool.
When it hot, the wires are cool, so I’m not concerned.
2019 AMG S 65 and too many other vehicles to list here in this small box
Originally Posted by Frenetic
Also, i noticed the charger gets really warm as well. At least initially, then it slightly cools off (but is still warm to the touch). Is that because of the different charging cycles or should i be concerned as well?
Warm to the touch is completely normal.
Originally Posted by Mikes62
Mine is actually hot to the touch. It’s been that way since I got it. I does cool off as the charging process continues, then when it’s fully charged, it’s cool.
When it hot, the wires are cool, so I’m not concerned.
You went from "Very Hot" to just "Hot" in your latest reply so I think it's more of a perception of what Hot is.
When Hot or Very Hot are used to describe the condition of an electronic device, it should be concerning.
Very Hot is Too Hot. Warm to touch is just right.
Mine is actually hot to the touch. It’s been that way since I got it. I does cool off as the charging process continues, then when it’s fully charged, it’s cool.
When it hot, the wires are cool, so I’m not concerned.
This is how hot mine gets when the battery indicator is at 50%. It’s hottest near the outlet plug side. Also, my battery was charging for 23 hours but the indicator never went above 80%.. I drove it a little while this morning and plugged it back in and it’s back down to 50% but the app says Charged.
So, I was in my garage just now and I just witnessed something interesting. Now my keys are 90 feet away in a faraday pouch. I heard my car do some random buzzing and whirring and I saw the charger light dip from 80% to 50% before my very eyes. Once it stopped, it immediately went back to 80%.
Why is my car doing these things? What is it doing? Why is not in sleep mode? Is this why that damn battery is constantly draining?
So, I was in my garage just now and I just witnessed something interesting. Now my keys are 90 feet away in a faraday pouch. I heard my car do some random buzzing and whirring and I saw the charger light dip from 80% to 50% before my very eyes. Once it stopped, it immediately went back to 80%.
Why is my car doing these things? What is it doing? Why is not in sleep mode? Is this why that damn battery is constantly draining?
When you opened your hood to charge your battery, did you also go to each hood latch and press them down two clicks? Doing that will simulate the hood being closed and the car can go into a sleep state since it's also in a secured state. You can verify the hood status by looking at the Mercedes Me app or check that your driver's display is not giving you a hood open warning. Doing this was the only way I was able to get my battery fully charged, 100% and consistently in maintenance mode for over a week; don't forget to pull the hood latch lever twice again so that you can close the hood when you are ready to remove the charger.
In lieu of using the faraday cage for your keys, you can also disable the keyless go/proximity key feature that is draining the batteries in both the car key and the car itself when their radios look for each other by:
2021-2022 W223 - Press the lock key twice in succession, the red light on the key will stay on for about 2 seconds indicating keyless go is disabled
2023+ W223 - Press and hold lock, then double press the unlock button while still holding lock at the same time
Since the procedure above is disabling keyless go for this one occurrence, you would need to press the unlock button to unlock the car. Unlocking the car with the key turns keyless go back on, so you have to repeat the procedure each time you want to disable it.
I can’t do that because the alligator clips for the charger stick out so much. I don’t have the post connectors, which i will likely buy.
The hood latch trick I noted above allows the car owner to keep the hood physically opened so that the alligator clips can be used to charge the car battery, but at the same time, the car thinks the hood is closed due to the car owner pressing down on both hood latch mechanisms 2 clicks, simulating what the physical hood would do to those latches when the hood is allowed to close. So after the hood latch trick, the car will be able to go into sleep mode since it thinks the car hood is closed and secured, but in reality, the hood is physically wide open and both the hood latch sensors have been set to the closed state by physically pressing the latches down 2 clicks.
I did this hood latch trick in my garage where I can securely leave my car hood open to charge the car battery for as long as I want. If you are in a situation where you can't leave the hood opened in a secure location to charge your car battery, then the battery post solution you suggested is the way to go.
So, I was in my garage just now and I just witnessed something interesting. Now my keys are 90 feet away in a faraday pouch. I heard my car do some random buzzing and whirring and I saw the charger light dip from 80% to 50% before my very eyes. Once it stopped, it immediately went back to 80%.
Why is my car doing these things? What is it doing? Why is not in sleep mode? Is this why that damn battery is constantly draining?
My wife keeps her keys in a Farady box away from the car, and double locks the car. Someone on this Forum mentioned that this helps.
It sounds like what you are experiencing is normal. I’d keep the keys farther away or get an actual Farady box that seals better? That might help and they are cheap on Amazon.
This is how hot mine gets when the battery indicator is at 50%. It’s hottest near the outlet plug side. Also, my battery was charging for 23 hours but the indicator never went above 80%.. I drove it a little while this morning and plugged it back in and it’s back down to 50% but the app says Charged.
I don’t have a Fluke to check the temp. of my charger, but 145 sounds about right.
I just had my yearly service yesterday and they told me there was a fault in my 12 V starter battery and they replaced it under warranty. No more partial charged in the app. By the way, a warning message never appeared in the car itself, just the app, yet my battery still tested bad.
I just had my yearly service yesterday and they told me there was a fault in my 12 V starter battery and they replaced it under warranty. No more partial charged in the app. By the way, a warning message never appeared in the car itself, just the app, yet my battery still tested bad.
Same for me - they replaced the12V battery in my 23 580 on its last B Service a few months ago.
Today I noticed Partially Charged 12v Battery in App. My 12v was replaced during CPO in December 2025. I drive the car once a week, usually. Do I need to invest in a Ctek/Mb Battery Tender. If/when I get one how often do I use it? I previously had a W221 and I never used one. I did see the following statement in the GLS Forum.
"Now I use a couple of CTEK maintainers, and I attach them twice a month and let them run for a day or more. If I'm going to be away for an extended period of time (2 weeks+) the CTEK is on duty full time. Lots of folks are using NOCO maintainers, but the important thing is NOT to use a "trickle charger," which will also overcharge a battery."
Also which Tender is most used with the W223? I see quite a few other talking about CTEK for AGM...Not Lithium. Thanks for your time
Today I noticed Partially Charged 12v Battery in App. My 12v was replaced during CPO in December 2025. I drive the car once a week, usually. Do I need to invest in a Ctek/Mb Battery Tender. If/when I get one how often do I use it? I previously had a W221 and I never used one. I did see the following statement in the GLS Forum.
"Now I use a couple of CTEK maintainers, and I attach them twice a month and let them run for a day or more. If I'm going to be away for an extended period of time (2 weeks+) the CTEK is on duty full time. Lots of folks are using NOCO maintainers, but the important thing is NOT to use a "trickle charger," which will also overcharge a battery."
Also which Tender is most used with the W223? I see quite a few other talking about CTEK for AGM...Not Lithium. Thanks for your time
Isn’t a “trickle charger” and “maintainer” the same thing in modern chargers? I bought the Mercedes one, which I believe is a rebadged Ctek, and it says in the manual that “…the battery charger can remain connected for months in ‘trickle charge’ mode.”
Today I noticed Partially Charged 12v Battery in App. My 12v was replaced during CPO in December 2025. I drive the car once a week, usually. Do I need to invest in a Ctek/Mb Battery Tender. If/when I get one how often do I use it? I previously had a W221 and I never used one. I did see the following statement in the GLS Forum.
"Now I use a couple of CTEK maintainers, and I attach them twice a month and let them run for a day or more. If I'm going to be away for an extended period of time (2 weeks+) the CTEK is on duty full time. Lots of folks are using NOCO maintainers, but the important thing is NOT to use a "trickle charger," which will also overcharge a battery."
Also which Tender is most used with the W223? I see quite a few other talking about CTEK for AGM...Not Lithium. Thanks for your time
The 12V battery in my W223 is AGM not lithium. The 48V battery is lithium and that is not the battery notification this thread is referring to
The 12V battery in my W223 is AGM not lithium. The 48V battery is lithium and that is not the battery notification this thread is referring to
Sparky thanks for the clarification. Now on to the other questions: I drive the car once a week, usually. Do I need to invest in a Ctek/Mb Battery Tender. If/when I get one how often do I use it?
Btw the app shows Charged now...not Partially Charged. I took it car wash less than 5 miles away and back.
On our W223 2022 after low or critically low12V battery charge state notifications on the App I have attempted to charge the 12V AGM battery with a well known NOCO Genius 10 charger using the MB recommended "posts" in the engine bay. Even when the charger is connected correctly there, set up properly for AGM, hood closed, keys stowed away in metal box, it never completes the charge and always sets an error message on the charger, then stops charging. Charger remains hot. Heck if left attached, it even discharges the 12V battery further to the point the doors won't open without the key.
The only way I can get the 12V AGM battery to fully re-charge is drive-it or charge the 12V battery from inside the trunk directly hooked up to the battery. This can take up to 24 hours depending on state of discharge to obtain a full charge. I know the charger is functioning properly as it works perfectly well on our other two MB's with AGMs & without the additional 48V lithium battery.
It's like the vehicles BCM (battery control module) is preventing the 12V battery from being charged properly from the engine bay; AGM trickle charge mode or 10 amp mode. 12V AGM battery has been replaced under warranty before & may need to be replaced again. Only 30K miles on the odometer.
Last edited by Sleeper Benz; Mar 29, 2026 at 11:09 AM.
Before they replaced my battery, I had the a similar issue: it would never fully charge. I only charged it via the engine bay posts. I would on occasion see the battery actually drain, at least according to the state of charge on MB’s charger. Aren’t there issues bypassing the battery control module by connecting it directly to the battery? I read it can accelerate the failure of the battery.
It does sound like your battery needs replacing. These 12-Volt AGM batteries just don’t seem to last very long. Not like the old days. I think it’s a combination of much higher loads in newer vehicles coupled with just crap quality in general for these batteries.
I usually disconnect the 12V AGM battery's negative cable before direct charging the battery in the trunk. I would believe that's enough isolation from the vehicles system to prevent any harm.
If this is the new normal, I may look into a dual AGM battery set-up if the vehicle's hardware & software are up to the task There is room in the lower trunk area next to the existing 12V AGM battery tub. You would just loose the plastic cover's cubby storage space.This would have to be an after-warranty modification of course.
I usually disconnect the 12V AGM battery's negative cable before direct charging the battery in the trunk. I would believe that's enough isolation from the vehicles system to prevent any harm.
It would be better to leave the negative cable connected while charging the 12 V battery. The point is that these new cars monitor battery current even when the car is in "deep sleep". The battery sensor does this and sends measurements to other control units when ignition is switched off. The car tries to measure accurately the battery SOC, not only by monitoring the battery voltage but also by measuring current to and from the battery all the time. Now if you disconnect the negative cable, the car is not able to measure the charge current from the trickle charger.
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There is room in the lower trunk area next to the existing 12V AGM battery tub. You would just loose the plastic cover's cubby storage space.This would have to be an after-warranty modification of course.
