Originally Posted by W206_Greece

The car is functioning properly, except for the battery issue, and had no problem starting the engine even with the battery at a critical state. So, it can wait for the time being.

Originally Posted by giovane

Dealership acknowledged the issue, and replaced the battery under warranty when I took the car in for 40k miles Service B.

However they had to deactivate all the Digital Extras and reactivate them to clear the error message in the app. Weird.

Originally Posted by W206_Greece

Hello to everyone,

I have been browsing the forum as a guest for quite some time and found many posts useful. I joined today to ask the community about a problem I have encountered with my C180 (W206), which has not been solved up to now.
I purchased the C180 in February 2024 (new from the local dealership), the car was built in the summer of 2023. Initially, I considered ordering a car with the additional equipment I would like to have, but due to long delivery time and a substantial discount on this already imported car, I decided to go for it.

I didn't encounter any problems up to the end of December 2024. As I use the car only for long distances, and not for driving around through the city because the size is not convenient, normally I travel about 300 km per week, these in a day or two. Then the car remains parked in a closed garage for about 6 to 7 days. At the end of December 2024, I received a message in the Mercedes app that the 12 V battery was low. This was the first time, the months before that the menu shown the battery fully charged even when I was abroad and the car was left for more than two weeks without driving it.

This behavior continued and now after five to six days the battery is at a critical level. I had the car checked at the dealership and they consider this a normal behavior. Their advice was to drive the car more frequently or to use a trickle charger.
I did use a high-end charger/trickle charger suitable for 12 V AGM batteries and it took a much longer time than expected based on charger specs to fully charge the battery (it was in moderately charge state when charging started).

Then, other problems started appearing, even though the battery appeared to be fully charged. The parking sensors lost part of their sensitivity and they operate much later than before. I noticed that because I have to maneuver the car through narrow space to park in my garage. Also, I drove the car for ~300 km and the lane keeping sensors and blind spot assist were not active at all. Then, suddenly, started working again. The car was restarted in between without any change. I contacted the dealership and they consider this to be due to not driving the car frequently (the battery was fully charged when this happened).

Now, after a day it becomes moderately charged, then with the car parked fully charged (!) without any charging, and then discharges again. I measured the voltage using a multimeter for some days and the reading were the following:
12.37 V (fully charged message, a few hours after driving the car for ~300 km)
11.97 V (moderately charged message)
12.30 V (fully charged message, with the car parked)
12.06 V (moderately charged message)
12.34 V (fully charged message)
11.71 V (moderately charged message)
Then drops further to low and critically charged state.

Next week the first service will take place and they will check the car again.

Did anyone have similar issues?
In my opinion, this is not an acceptable behavior for a new car. Any thoughts and advice would be appreciated.

Originally Posted by carlbid

I’ve seen similar issues on newer models, and in many cases the root cause turned out to be a parasitic drain from one of the onboard systems that kept running even when the car was “off.” This slow drain can take the battery from fully charged to critically low in just a few days. Dealerships sometimes dismiss it as “normal” or due to infrequent use, but in reality a proper load test and a parasitic draw test can pinpoint the problem. In my own case, I had to push my dealer quite a bit before they found the fault. It’s a bit like making a big purchase without a detailed inspection. Where hidden issues can remain out of sight until they cause much bigger problems later on. For a new car, that’s not something I’d consider acceptable.

Originally Posted by carlbid

It does sound like you’re dealing with more than “normal behavior” here. A healthy new AGM 12 V battery in a W206 shouldn’t be dropping to critical charge within 5–6 days, especially if you’ve been doing 300 km drives that should give the alternator plenty of time to recharge it.

A few things stand out from your description:

• Rapid voltage drop – Anything under ~12.2 V after sitting for a day suggests the battery isn’t holding charge well or there’s a parasitic drain.
  
• Inconsistent “fully charged” readings – The car’s battery management system may be giving false status updates, possibly due to software glitches.
  
• Electronics acting up – Safety systems like parking sensors and lane assist can disable themselves if the system voltage drops below a certain threshold, even briefly.
  

For your upcoming service, I’d recommend asking them to:

1. Do a proper parasitic draw test – This will show if there’s an excessive drain when the car is off.
   
2. Load test the battery – Even new batteries can be faulty or damaged.
   
3. Check for software updates – Mercedes sometimes releases firmware fixes for battery management quirks.
   
4. Inspect ground connections and charging voltage – Poor grounds or alternator regulation issues can cause partial charging.
   

If they still call it “normal,” you might consider requesting the findings in writing and escalating to Mercedes customer service. A new premium car shouldn’t require constant charging just to keep basic systems working.