Anyone else feel like the battery charging on these mild hybrids leaves a lot to be desired? The way I understand how this works is that the ISG charges the 48 Volt battery and then the 48 Volt battery charges the 12 Volt battery via a DC to DC converter.

Does the ISG only charge during regenerative braking? If that is the case, then I can see why the 12 Volt battery charging sucks, especially if you do any spirited driving (which drains the 48 Volt battery) and/or just don’t brake much. Am I correct in my assumption?

 

That's a very good question.
But if the only 12V power source is the 48V which is charged only via generative braking, then there's no way it can sustain the power load during long highway drives (no braking)
My guess is, it HAS to use the ISG to generate power.

 

It depends on the options too, if it has E-ABC, it has to take care of that as well.

 

According to this article, it does only charge during braking or coasting, which explains a lot. Unlike a belt driven car, it’s not how long you drive that will determine how much you charge the 12 Volt battery, but how much and for how long you brake and coast. In other words, every mild hybrid owner should buy a battery charger.

https://www.ctek.com/uk/news/how-to-...-a-mild-hybrid

Does anyone know how the 12 Volt system is charged in Mercedes plug-in hybrids? Also a DC to DC converter?

 

There's a comprehensive article on the various implementations of MH systems at https://x-engineer.org/mild-hybrid-e...es-mhev-types/. It would seem that the ISG can be engaged at any time needed (just like a conventional belt driven alternator) to charge the 48V and 12V batteries.

 

Thanks for the article. I just kind of glanced at it and it seems to cover Audi’s belt-driven starter-generator versus our belt less ISG. Does that belt make a difference on when it charges?

 

I don't own a MH vehicle, so I know only what I read about it. Whether the charging source is belt driven or gear driven shouldn't alter its ability to deliver charging current to the battery when it's needed, although the charging control algorithms might be different. My understanding is the the ISG MH version completely eliminates the engine's serpentine belt, and functions normally belt driven, such as A/C and the water pump, have integral 48 volt electric motors. Long term, 12 volt batteries and accessories will be obsoleted, and automobiles will be entirely 48 volt based.

 

The CTEK article is vague, perhaps intentionally to promote their sales. They actually don't say the 48 V battery being only charge through regenerative braking. Anyway, the 48 V battery (and the 12 V battery via the DC converter) is charged by the ISG if needed (using ICE power if needed).

Seems though the 12 V battery charging control isn't ideal. A lot of complaints about (almost) dead batteries and other problems. In the past the 12 V battery was intentionally kept less than fully charged to allow some minor energy recovery from braking which would not be needed with (mild or plug-in) hybrids as the higher voltage (and capacity) battery handles that.

 

Yeah, the 12 Volt battery charging is abysmal in my opinion. I’m really curious how the battery management is handled. The 12 Volt battery isn’t charged directly from the ISG; it’s charged from the 48 Volt battery. That 48 Volt battery powers a lot: the 12 Volt battery, all old belt-driven accessories like the water pump and ac compressor, and the EQ boost. It’s too much and why the damn 12 Volt battery constantly needs separate charging.

 

I'm skeptical that sufficient charging could be obtained exclusively through braking recuperation. If you have a voltmeter, it would be interesting to connect it to the battery, put the voltmeter on the passenger seat and watch the battery's terminal voltage while driving. You should see about 56 volts +/- 2 volts during braking and any other time charging is occurring.

 

15 months and 17,000 miles of driving this car I have never had any issue with 12v battery charging or ever needed a battery charger. When you say the charging is "abysmal", what do you base that on?

 

Think the main concern is not driving for a few days and/or driving short trips, frequent engine start/stops or bad batch of batteries, or lack of software updates that fixed the door module drain and other parasitic drain such as those from a dashcam. If those are not factors, the car should maintain its charge.

 

I have left mine for weeks at a time, driven short trips, been in and out of it a bunch over the course of the same drive and have never had any issues. This has got to be something that is wrong with some cars and not with others.

 

I see then it is probably a bad battery for the other folks.

 

I owned a GLE 450 2021 for a couple of years. On that vehicle on the information screen in the MBUX that displayed the horsepower - torque - other stuff it also displayed the 12V system voltage. After starting it would display 14.7V and after driving for a while it would drop to 12.8V. When I traded it on the 2021 GLE63 I noticed that on the AMG that same screen did not display voltage. I mentioned it to the SA but of course he did not know why.
I believe the rotation of the engine does charge the batteries. I believe all of the systems and software variations of the different models vary enough that few if any persons at a dealership have a full comprehension of each model.
I do not drive the S580 often and I usually keep it on a smart charger and I notice every time when I disconnect and reconnect my charger while the vehicle is locked and appearing "asleep" my 2022 S580 the amps kick back up and I hear relays click and stuff happen. No idea why or what is occuring. The keys have been double clicked off and are away in the faraday box. Nothing inside the vehicle looks to activate when this occurs. I just notice the trickle charger shows everything charged and maintained so maybe once a week as I pass by it in the garage I disconnect and reconnect and then there are the clicks and sounds and the charger ramps up for a bit before going back to trickle state. Obviously sensors detect the connection and the software decides to do something. I have experinced the exact same clicks and such with the GLE63.
I will add that the GLE63 when shut down after driving makes noise the S580 does not. I assume there is an electric drive that circulates the coolant or oil to the turbos or something for a period of time after shutdown. As they both have the dual turbo setup I have wondered why the S does not make that same noise. Perhaps due to the dry sump vs wet sump differences. Responses received from my inquiries of SA's leaves much to be desired.

 

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On the GLE (never attempted yet in the S) in the workshop menu you can access the 48V system and view realtime the recuperation voltage, amperage and state of charge.
SOC appears to try to maintain in the 70%. Amperage during recuperation exceeded my expectations and I have seen well over 200A for brief periods

 

My S580 runs the fans for a good while after shutdown

 

As does mine.
I'm sure the engine room get plenty hot with the 'hot V' turbo setup.

 

Thanks for your reply, does the fan come on for a long time all the time or occasionally?

 

Just an update. I charged it over the course of a week. The first time it charged for 26 continuous hours and it still didn’t max out, however, the app no longer said partially charged. But, after two days of driving, it went back to partially charged. I then started charging it again. The first stint was 18 hours without maxing out. Only after 28 more hours did it finally hit trickle mode. I’ve driven it for a week and hasn’t dropped back to partially charged yet.

I don’t drive much. My commute is 12 miles each way half of it on the freeway and I only commute two or three days a week. Other than that I’ll drive it a few miles here and there. Prior to my Mercedes, my non-mild hybrid BMW did the same amount of driving without ever having a low battery warning.

 

My driving is very similar to yours and I never get any low battery warnings. My guess is you have a bad 12V battery.

 

I don’t think so, because I never actually got a warning in the car, only the app and the partially charged warning, which despite my best efforts of doing a “long drive,” would never go away. I’ve read here that partially charged batteries really end up shortening its life, which is what I want to avoid and no amount of driving would fix (hence my complaints about the ISG’s lack of charging capability). Only after nearly 70 freaking hours of charging with a battery charger did it go away lol.

 

I never get a warning from the app either. If all you are getting is an app warning and you see no drivability issues I wouldn't even give it a second thought. I don't think there is any issue with the charging if you're not experiencing any battery charge issues.

Just drive your car and don't worry about it. Thats a lot of effort to prolong the life of a $300 12v battery that almost certainly won't fail until after you no longer have the car since you lease.

 

Yeah, I’ve been getting 12 Volt battery low messages and if you check the services section in the app, my battery would never leave partially charged no matter how long I tried driving. Check yours and make sure it’s not partially charged as that is detrimental to the battery, at least I’ve read that here.