Lately I'm getting a 12v warning status when I start my truck. No codes or CEL, but I want to swap it before it becomes a problem. Is there any coding required in a 2021 GLC63 to swap the battery?

I was getting the same alerts regarding the 12v battery. I have the original (AGM) battery in my '21 GLC43. My dealer told me to get a battery tender and try that. Worked like a charm. The AGM batteries require quite a bit of daily driving to keep them fully charged to the point you won't get the 12v warning. My daily drive to work is 11 miles each way and that (evidentially) isn't enough to fully keep the 12v battery charged. For the record, the battery tender was much cheaper than a new battery.....

My AGM battery was half dead but never drop any messages on dash. In cold mornings it starts the car after 3-4 attempts and start/stop never worked. Bought new Bosch and happy days now.

I could never understand why M-B would not display the state of charge (SOC) of the 12 V battery in terms of volts and %; it's such a simple and helpful feature, especially that the open-circuit voltage (OC) of an AGM battery at rest is very well related to its SOC.

Every phone has this function and display,;why can't they M-B and all the other ICE automakers) add it to the display? All EVs have it...

Because cranking an engine over is far different than powering an EV or a phone. Starting an engine, especially a big diesel or V8 takes gobs of power. If you were to act as a conductor between the battery and the starter during starting, you would die, That's how much power they put out. You do that with a Lithium battery, the battery would not last very long. Lithium batteries are designed for low power usage over a long period of time (yes, I know that there are some specialty lithium batteries that are designed for engine starting, but that aren't that popular). As such, grabbing the state of charge for these starter batteries using conventional methods is inaccurate. Many mechanics are finding this out. These new digital internal resistance charge testers are woefully inaccurate for borderline batteries. The accepted method for testing battery capacity is to test the direct amps the battery can generate..and the only way you can do this is under load. This means some kind of load that's NOT the starter to test the battery amperage. This is usually in the form of a carbon pile that you dump the voltage into, or huge heater coils that light up to create a load. Do you remember those Duracel batteries that had the strip on the side or came with a little strip in the package? You pushed your thumb on one dot and your finger on the other dot and the strip changed color? It did this by heat. That strip was a strip of carbon that put a load on the battery to determine its charge. Today, you can get obvious failed batteries by testing it's resistance....but this method does not work if all the battery needs is a quick charge.

I agree with what you wrote, but you may notice that I wrote about testing the state of charge of the battery, not its health, capacity, internal resistance or its cranking power. The OCV value at rest simply tells you if the battery is charged or not, nothing else--but is extremely simple (voltmeter) to measure. I have an OCV vs SOC chart on my garage wall to help me decide if the batteries need a charge.

I agree with what you wrote, but you may notice that I wrote about testing the state of charge of the battery, not its health, capacity, internal resistance or its cranking power. The OCV value at rest simply tells you if the battery is charged or not, nothing else--but is extremely simple (voltmeter) to measure. I have an OCV vs SOC chart on my garage wall to help me decide if the batteries need a charge. See the tables here

https://www.jackery.com/blogs/knowle...-voltage-chart