I took in the GLB 35 for ongoing issues with the 12-V battery draining (issues since beginning of '25) and service advisor found the below brand new campaign which I wanted to share. This also affects CLA and GLA.

#2025100004
Update 48-V On-Board Electrical System Battery Software.

Mercedes-Benz AG, the manufacturer o f Mercedes-Benz vehicles, has determined that on certain
subject vehicles, the 48-V on-board electrical system battery software might not meet current
production specifications. A communication error may occur when reactivating the 48V lithium-ion
battery during reinitialization. The system might detect and store this error, causing the malfunction
indicator lamp t o illuminate unnecessarily.

Thanks for the heads up. My MB dealership reached out and had a software update pushed to my glb35. Not experienced any battery related issues from owning from new.

Hopefully, that'll solve those with battery issues.

For those owners of MBs with problematic mild hybrid 48 volt battery systems who hope the next software update remedies their problems, the following information is provided to help you better understand the nature of the underlying issues.




The illustration above shows two bytes of software each comprising 8 bits of 1's and 0's. The top byte is genuine MB software downloaded from a 2016 GLS450. Despite this vehicle having been driven over 87,000 miles, one can observe the integrity in the shape and form of the "1"s and "0"s. The bottom byte was downloaded from a 2024 G550 equipped with the 48 volt mild hybrid system. It doesn't require the trained eye of a certified Mercedes Benz master mechanic to identify certain irregularities in the shape and form of these bits, and conclude that these could well be the source of vehicle reliability problems.

Beginning with the left-most "1", it's immediately noticeable that the bit has excessive wear and distortion in its shape. This "1" was emitted by the voltage regulator, sourced from a MB OE supplier. This supplier, without the approval of MB, began outsourcing its software code from a company believed to reside somewhere in eastern Europe. In an effort to reduce cost, this eastern European code provider used low quality bits in its software, which are believed to originate in China, and are counterfeit despite being labeled "genuine MB". These bits are not able to survive the rigors of the high speed CAN buses in MB vehicles, and this disintegration after only 8,000 miles is quite apparent. Fortunately, MB engineers have released a service pack to the MB SDS that is able to flush 99.9% of these sub-standard bits out of your vehicle's ECUs and SAMs using the OBDII connection. This service takes less than an hour, can be performed during any scheduled A or B service, and (of course) will be done at no charge to the owner.

The next anomaly involves the upside down "1" digit at the fourth location from the left. MB takes complete ownership of this defect in admitting it mistakenly assigned a coding project to an unqualified junior level engineer. The code requirement was to invert this bit, which to an experienced software engineer means converting a "1" to a "0" or converting a "0" to a "1". This engineer misunderstood his assignment, and his code resulted in turning the bit upside down instead. Inexplicably, this upside down "1" can mysteriously, and without warning or reason, correct its orientation by righting itself. MB believes this could behind the mild hybrid systems that suddenly shut down the vehicle on the expressway without warning, yet allow the car to return to normal operation after sitting for 5 minutes with the ignition off.

Finally, there's the right-most bit "0" which is noticeably smaller than the other bits. This bit is exemplary of MB's vehicle weight reduction (VWR) project which seeks to improve fuel economy through the utilization of smaller software bits that could shave off as much as 0.0001% of the vehicle's GVWR. While still experimental, early results are showing problems with the small bits in that they fail to arrive at their destination (which is what happened to the bit to the immediate left). Investigations to date reveal these bits disappear only on CAN buses that exceed 2 meters in length. A software update is expected soon that will ensure small bits are used only on short distance CAN connections. If you've experienced a navigation screen that suddenly goes blank, it's likely a consequence of these small disappearing bits.

This technical explanation is probably difficult for many of you to comprehend, but you might want to print out a copy to give to your service manager when you schedule service for your software update. He/she will thank you, and will then be aptly prepared for the tech-savvy MB owner who tries to ask embarrassing questions that he/she would otherwise be unable to answer.

I just replaced my battery because the dealer told me mine was dead. I’ve had notifications from the system forever that my battery was low. Is this a different issue or should I contact my dealer?

I would contact them, yes. According to my dealer, it's a separate issue. My GLB 35 has now been in shop for 2.5 weeks to receive the 48V update, but also continued issues with the 12V battery. They don't know what's wrong—they say the 12V is 'fine' but it's not holding a charge (only allows up to like 70%). From day one, I've asked them to replace the battery since the car was on showroom floor for one year before sale to me, but they still have not done so. I'll keep this post updated when I know more, if I'm not dead from stress.