2021 GLB FWD. I was having issues with the start/stop feature not working. I would drive for 80+ miles and it still wouldn't function. Also, the battery voltage wouldn't hold over a few days of not driving. 12.3 volts dropping to 11.9 volts

The interior lights were doing weird things also. Open the front drivers and passenger doors and the lights would not come on. Close the doors and they would come on. Low voltage causes weird things to happen.

Been dealing with it for a few months so took it in to troubleshoot. I suspected a bad battery and that was the problem. Replaced under warranty. Car build date 11/20.

Had the same problem with the S/S on my wife's 2018 Ford Escape. 1st battery lasted only 20 months, the 2nd about the same. Guess the quality of battery's is suspect anymore. They live in a hot environment under the hood which I think degrades their life cycle. I had a 2015 Jeep Grand Cherokee for 5 years and never replaced the battery. It was located under the passenger's seat though.

Anyone else had the same issue with limited life of the battery?

 

No issues so far with the battery. Auxiliary battery lasted 8 years on the GLK. Main battery was replaced at 7 years under regular maintenance cycle...Hopefully it will be same for GLB...

 

We’ve had the GLB250 for about 1½ years & 30,000 miles. No battery problems. The battery in my C250 is 8 years old.

 

I assume in the GLB the start/stop function uses the main battery, not an auxiliary battery?

 

I don't know GLB, but there was a very happy posting on GLK forum that his GLK start/stop function was not working since GLK auxiliary battery was dead. Quick search says:

https://eurautoshop.com/fixing-the-a...in-a-mercedes/
"The auxiliary battery is a backup for the main battery. It does a number of jobs depending on what model of car it’s installed in. These range from powering electrical accessories like the radio/infotainment to operating the engine stop-start system. (To be accurate, in a few Mercedes-Benz models it’s actually a capacitor, which is another device for storing electricity.) Like the main battery, the auxiliary battery is charged when the engine is running. And just like that battery, it lasts around four to six years. When it can’t hold a charge the computer pops up that malfunction message."

https://www.youcanic.com/mercedes-be...y-malfunction/
"One of the most important functions of the auxiliary battery is to operate the gear shift selector when the main car battery dies. Mercedes-Benz has what is known as a drive-by-wire. This means your gear select shifter is electronically controlled. If the main battery dies, you can no longer control the shifter and place the vehicle in Park. Since there is an auxiliary battery, you can still shift to Park even if the main battery dies. This is a safety feature. Depending on the model, the auxiliary battery can operate additional functions and accessories such as sensors, COMAND, heated seats, radars, stop-start functions, etc."

 

Looking online I can't get a definitive answer whether the GLB has a Aux. battery. You tube shows replacing it in the sedans and it's located in the trunk.

I don't think there is one located in the cargo area that I can see.

​​​​​​​Videos also mention a display in the dash saying auxiliary battery malfunction which I didn't have.

 

The aux battery specified for GLB has been in use by MB since 2005:

https://mbparts.mbusa.com/v-2021-mer...rical--battery


https://mbparts.mbusa.com/oem-parts/...y-000000004039

• SKU:000000-004039
• Positions: Rear
• Description: Auxiliary. Back-Up. 1.2 AH. Conventional. back-up

A class has it below the center console:
https://www.aclassclub.co.uk/threads...ocation.20501/


GLB has it below the center console also (@ 1:53):

 

I had short battery life on almost all of my cars (Toyota's and Honda's). Lasted approximately 2-3 years, and then needed replacement. I read years ago that manufacturers undersize their batteries, which causes them to fail prematurely. There is also evaporation issue with acid batteries that are not fully sealed. Most of the batteries have caps or screws on top, and when battery starts to act up, open and check if the liquid level is low. It should be filled to the top. If it is not, add distilled water.

 

The GLB has an auxiliary battery but at 1.2 ah, it’s smaller than the 12 ah batteries that supported the auxiliary transmission pump on the stop/start vehicles (unless that’s a typo). The DCT8 in the GLB either doesn’t need it or uses the main battery. I can’t find enough information online about the GLB systems to determine. One of my indie mechanic friends said I should talk to him next time I’m in for service and he would explain how the vehicles assembled by COMPAS are very different from my older Benzes.

 

I'll look under the hood to see where this aux. battery is mounted per the diagram. Being that small what's it's exact purpose? Is it for S/S only?

Other S/S aux batteries' I've seen mount in the truck (Chevrolet) and are about 1/2 the size of the main battery.

 

The auxiliary battery is not in the passenger foot well, like in GLA, I opened a fuse box there and did not see the battery cover. Unless it is behind the fuse box. One of the YouTube shorts videos point the battery location to the center console. The GLB battery diagram is very confusing, as it shows it next tot the main battery, however that could be just a one line diagram and not exactly pointing to a auxiliary battery location.

 

It is confusing.
I think I will check with the service dept. just for curiosity on the location and the purpose of the aux. battery.

 

Service rep called me to check on how the car was operating after the 12 volt starter battery replacement.

I told him everything is working as needed. I asked about the aux. battery and he told me it's main purpose is to provide voltage to be able to shift the car out of park if the 12 volt battery failed completely.

 

Never leave your keys in the car or hanging up within 50 feet - better to put them in a foil pouch or sleeve. The car and fob love to communicate with each other. This impacts key fob battery and car battery life.

My evidence is anecdotal over 16 years including a 2006 Corvette, Nissans, BMWs, my ex-wife leaving fobs in the tire well or at the door within 15 feet of the car, and my two MBs.

 

I've never left keys in the car. This issue was basically from the 1st week I bought it used as a dealer loaner. Took it in the 1st month I owned it and they said nothing was wrong. Ignore the app warnings, etc.

For whatever reason the battery did go bad. My key fob has to be within a couple of feet for the touch locks to work. I lay it on the workbench 6 ft. away and it's not talking to the car, no locks etc.

Battery's live in a very hot environment and heat is a killer on battery life. I honestly don't think the quality is there in today's battery's. In the AGM type anyway. We'll see how this one holds up. Thanks for your input.

 

Bringing up an old thread, but I think I have some relevant info and a question or two.
Our '21 GLB250 has 65,000 miles on it and has been rock solid except for the head replacement issue common to the M260 engines. Just today my wife got a message in both the instrument cluster and the message center to the effect of " Battery warning. Stop your vehicle somewhere safe with the engine running." I checked the system and the alternator is putting out 14.8 V. The battery drops to 11.2 V on starting and takes 30 seconds to recover. It also drops to 12.1 V with the engine off and the driver's door open. The start/stop hasn't worked for a few months now. It's the original battery and is 3 years 3 months old. I am sure that it needs replacement.

Now my questions:
1-Can an aftermarket battery be used? The BCM sits on top of the battery and is contoured to the top of the VARTA battery case. An aftermarket one would need the same contour.
2-The GLB does, in fact, have an auxiliary battery. It's a small 1.2 AH battery in the console. Has anyone ever seen a warning that it's bad and had to replace it?