I wanted to test if my Ctek trickle charger works with my 2025 E450.
I hooked it up directly to the battery in the trunk and within an hour I got a message on my app that the 12 V battery is extremely low in charge.I disconnected the charger and I will ask Mercedes Service on Monday about this.I think that the charger somehow fools the Computer that thinks that the battery is discharged for some reason.I do need the trickle charger to work since I will not drive the car for about five weeks

I have used the Chek charger to trigger charge 2024 E350 with no issue, although only through the regular charging posts under the hood but not directly attaching the charger to the battery in the trunk. I do plan on attaching a pair of permanent charging wires directly to the battery for easier trickle charging and will test that out later (I have it set up that way on the S-class with no issue).

Just curious: Did the car battery actually get discharged or just a false alarm that triggered an alert of the battery being low on charge?

once I disconnected the charger, I checked the app 10 minutes later and it didn’t show the alert anymore so to me it seems like the cars Computer is getting confused.Actually had a tech at Mercedes-Benz service hook up the permanent leads to the battery since it wasn’t simple to hook up the positive lead.He actually had to take the positive lead off the battery.Once he started the car he got a check engine light.
He did a scan which didn’t find anything and then wiped the error message.

Something odd here. I have my plug-in hybrid often in the garage for weeks and at times I get the 12 V battery partially charged status (not the critical level alert). I then hook up my CTEK to the jump start poles at the engine bay and after a while MB Me reports the battery (fully) charged. So does CTEK obviously.

Either the charger was not correctly connected or just a coincidence, sometimes the app status is not up-to-date.

Why do you want to charge at the battery terminals instead of through the engine bay terminals?

I think the owner's manual says to use the engine bay terminals for trickle charging.

Correct..

While it is possible to trickle charge through the charging posts under the hood of the car, it is much more convenient to be able to charge through wires permanently attached directly to the battery terminals and leave them hanging out in the trunk (or even leave them hanging outside the truck with the trunk lid closed). This way eliminates the necessity to open the hood and attach the charging wires every time the car needs to be trickle charged. Although I have not tried it on my 2025 E450, I have this setup on my S-class with no issues at all (many others have posted similar experiences).

update
I brought the car back to my dealer and a very nice mechanic helped me.The battery tender direct connection to the battery was connected to the positive and negative terminals of the battery.He suggested to take the negative cable and connect it to a grounded screw in the trunk.After trickle charging the car overnight, I did not get any message of low-voltage so hopefully that solved the problem.I will try one more time tonight

Very good to hear everything seems to work now as expected. That is exactly how I hooked up my trickle charger directly to the battery on my S-class (to positive terminal and a grounding location but not the negative terminal). Please keep us updated of any new and possible unexpected development as I also plan on having a similar setup in my 2025 E450.

Very interesting post and the responses shared had me double guessing myself. I've used Battery Tender products for years and have always hardwired the connections direct to each battery terminal. This post lead me to read the instructions and per Battery Tender - you connect the positive to the battery and the negative to a chassis ground just as described above. Although I've never had a problem, including the 2025 E 53, I'm in the process of changing all ground connections to the chassis.

Update and not to add to the confusion. Battery Tender chargers offer conflicting advice across the various instructions you can download. Varying from direct to terminals; or direct to positive terminal and negative to chassis for Lead Acid batteries only as a UL recommendation or just their own recommendation. The Ferrari battery location is in the passenger footwell and not many options other than direct to the terminals. It has been that way for 10+ years and the last battery lasted 8 years. The E 53 battery is in the passenger cowl location like the past e-classes and the negative cable comes off the battery, makes a loop and connects to the chassis. Approximate length of the negative cable is 10 inches or less. The bolt fastening the negative cable to the chassis is well done. Painted with no tool marks, along with other obvious grounds. I'm reluctant to relocate the ground as I can't imagine the car or charger would know the difference and I don't want markings to the chassis hardware. I'm leaving well enough alone as I'm not experiencing any issues.

I was successful in attaching a set of permanent charging cables to the 12V battery in the trunk of my 2025 W214 E450 for trickle charging.
My experiences:
1. To gain access to the battery, it is necessary to lift up the covering in the trunk which, unlike in my S-class, is not held down by screws or tabs. The trunk covering can be lifted up by freeing (plastic trim pry tool would be helpful) and pulling it up from the two sides and bottom end of the trunk. The top part of the covering is held down much more tightly to the car but it does not have to be completely freed up to gain access to the battery for the purpose of attaching the permanent charging wires.
2. Before detaching any existing battery cables on the car, it is always advisable to provide a secondary 12V power source during the entire process (e.g. through the charging posts underneath the hood) so as to avoid issues due to loss of power to various computer accessories.
3. The positive end of the permanent charging wire can be hooked up to the battery through the side terminal attachment point (where a small wire is attached on the side of battery positive terminal, and there is no need to loosen the main positive screw directly).
4. For negative wire, unscrew and attach to the neutral/negative post on top of trunk (no need to loosen the main negative screw directly on battery terminal).
5. A plastic pry tool is very helpful in tucking the trunk covering underneath the two sides and especially bottom end of trunk.

No check engine or other warning signals were triggered throughout the entire process and I have been able to fully charge the vehicle using a Ctek trickle charger/maintainer. The obvious benefit of this permanent setup is that it eliminates the need to open up the hood and attach charging cables to the regular charging posts every time for car charging.

Good job any pictures by chance?

https://www.mercedes-benz.ca/en/owne...he-12v-battery

Any trickle chargers recommendations? I heard of Noco Genius 5, CTEK, Bosch recommended, any other models or specific models?

I like Battery Tender brand which I use on every other car, except the E 53, which uses a MB branded CTEK. No technical reason - just a good deal.

I've never needed a trickle charger even though I have parked my car for 30 days without any issues.
I have enabled hibernate mode in the settings menu. It shuts down non-essential systems to conserve energy.

Thanks, sadly standby mode is not present in the menus of my car, it is a Canadian vehicle.

Thanks, I went ahead and ordered As I have been driving less lately.

I’ve used Battery Tenders for years on motorcycles, cars and my riding mower. I currently have one on my E450 because I haven’t driven it in a couple of weeks and the app showed partially charged. Never had a problem with one.

Thanks, will look at those as well.

Did anyone confirmed if MB only charges the W214's 12V battery to 80% to save gas hence why using CTEK on the W214 might be necessary to bring it to 100%?

Have never heard of it. 80% SOC for a PHEV or EV makes sense. But 12v accessory or starter battery would put it at ~10volts (If I'm mathing correctly) and would register as a low battery.

There is a small drop in voltage, but it is not equivalent to the percentage SOC drop. An 80% SOC battery will have a voltage of ~12.5 to 12.6 when the engine is off.