edpare

2021 GLC 300 : analog-style drivers guages has "charge" as a continuation of instantaneous mpg indicator. What is it showing me?

W205C43PFL

It just means the alternator is doing its thing, since your vehicle isn't an electric vehicle or hybrid vehicle, it wouldn't have regenerative braking so in your case it is the alternator charging the battery.

edpare

Been watching the behavior of this little guage: it only shows green for a few seconds and only when consumption guage shows "999" mpg. Since I don't have regen and since my alternator is always outputting 14+ V, the system must be checking the status of SOMETHING, perhaps that secret little starting battery I use so often with the default eco stop/start function?

W205C43PFL

Make sense that the consumption goes up because if you are stopped, you are not moving and effectively doing 0 miles yet still using fuel.

edpare

I didn't explain that well: 999 mpg only occurs while decelerating with foot off the throttle; like going downhill in gear.

W205C43PFL

I see, thanks for the follow up. If you haven't notice, putting the vehicle in glide mode/coast mode the green charge will show up as well. The green charge also shows up when the vehicle has completely stopped right?

edpare

Putting vehicle in glide/coast mode does not bring up green bar. Only deceleration with zero throttle brings it out and then only briefly.

W205C43PFL

Hmmm, I recall that it displays charge and the green bar shows up on my 2017 (sedan) during coasting with the sailing boat icon but I have a C 43 but should be the same, I need to check to see if I remembered it correctly next time I take a drive.
Have you scanned the vehicle for any codes just in case there might be (as in a possibility of) a slight malfunction?

Teckno

I think all this is related to the ‘secret battery’ !!
the charge indicator that disappears refers to charging up the AUX Battery that in reality is a small black box hidden under footwell carpet in passenger side that houses a capacitor.
In reality it is a voltage regulator.
These last around 4 to 6 years before needing replacement - the capacitor gives up and needs replacing.
If the car battery degrades or needs charging the stop/start function stops the alternator will never fully charge up the main battery due to AGM construction and higher volts needed.
Regular evening charging of main battery with a smart battery charger, kike CTEK, will lengthen battery, Volt regulator and minimise weird electronic issues that go away when main battery fully charged.

W205C43PFL

Thanks for chiming in, OP mentioned that earlier though.

edpare

Haven't checked for a code. I don't think anything is wrong; but I do think I discovered one of those "Mercedes Mystery" behaviors that I associate with owning a Merc.

W205C43PFL

Yup, exactly. I wouldn't worry about it unless you clearly see something wrong like unable to start a vehicle, CEL, etc. I believe everything is working as intended. I will let you know if I see the same behaviour on my 2017, been getting blizzards lately in my area so the vehicle is taking a break in the garage. That being said, I had a pre-facelift C-Class so it might have changed so it is not exactly oranges to oranges comparison.

W205C43PFL

OP, here is an excellent post by superswiss explaining how it all works: https://mbworld.org/forums/s-class-w...ml#post8505582

edpare

Great article, thanks for the url. Takes me further on my quest but now I have more questions. "the alternator never actually fully charges them to leave some room for recuperation" Huh? Why not? Why is the period of increased charge relegated to only throttle-off deceleration? And, isn't this behavior EXACTLY how regeneration works?

superswiss

Yes, it's a mild form of recuperation. Ever since car manufacturers replaced belt driven components in modern cars with electric equivalents such as electric power steering, electric on-demand oil pumps etc. there's increased demand for electric power and also to really reduce fuel consumption, the alternator periodically gets decoupled from the engine and the electrics are powered from the battery. The decoupling reduces drag on the engine, hence saving fuel. So just like in electric cars, it makes sense to recuperate some of the kinetic energy when coasting and put it back into the 12V battery so it can later be used to power these electric components with the alternator decoupled. So when you see that charge indicator, it's just like in an EV. It recuperates some of the energy by increasing the charge to the 12V battery. You won't see the charge indicator when glide mode is active, as then the engine is decoupled from the transmission and idles, so there's no recuperation.

superswiss

No, the charge green bar doesn't show when you are actually sailing/gliding. To clarify the difference, during the charge phase that's indicated with the green bar, no fuel is being burned, so the engine is kept rotating purely by the momentum of the car. Fuel injection is cut off, so it truly is recuperation as the momentum of the car rotates the engine, which then charges the battery via the alternator. When gliding however, the engine is decoupled from the transmission, and it has to burn fuel in order to keep idling. So gliding is not necessarily more efficient than coasting. Some electric cars therefore also have smart algorithms that decide when gliding is more efficient than recuperating.

edpare

Assimilating........

And I wonder how I can access "the workshop menu" with those nifty stats. I can't see my state of charge on mercedes me app.

superswiss

I posted the instructions in another thread: https://mbworld.org/forums/w213-amg/...ml#post8504964

W205C43PFL

Thanks superswiss for chiming in, I learned a lot and I am sure OP did too.

OP, the alternative way is to view the battery stats in Engine data, so that is another option if you want.