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Trying to replicate the scenario where it would do the typical 12v during driving but so far just 1 driving cycle did that.
You're in the right place for self-help:
-- The long answers have been well detailed...
-- The short answer is you may seek is :
ALT voltage not below 12.6.Volts
BATT currents not above 15.Amps
In this thread contributors are experimenting a self-regulated Valeo ALT without LIN (aka. "ALT-LIN") to bypass marginal R-SAM CAN-B quiet (fault-free) dysfunctions during the remote float voltage control aka. "YOYO": drain by driving.
> Personal Opinions... not advice
experimental modification are not for everyone.
You need to understand what you are stepping into... study a bit for full benefits else unrelated surprises can be misconstrued.
My non-profesional opinion... as far as I believe MB W212 Limp-Mode snow-***** are not directly linked to low voltage alone but caused a collective network disruption of CAN-C courtesey of CGW upset by solderless CAN-B chaos assaulting CGW to read wheel speeds, tranny gear selection, PRND location.... Understand that CAN-B traffic interrogating CAN-C VIP's is disrupting bi-directional traffic from Engine <--> Tranny.
CAN-B modules are setup to be voltage sensitive on different branches with different node length... this chassis has to become unstable (reboot!).
This is not designed to be a Toyota: ENJOY the bleeding edge challenges.
Last edited by CaliBenzDriver; Oct 31, 2025 at 12:08 AM.
Still observing and reporting but it is still the same situation
Random days I have 14.4v - 14.7 on the entire drive cycle (even with headlights + AC OFF)
Other days it does the yo-yo similar to eco profiles
The only difference is all of my eco parameters are disabled (non functioning button+light) a certain ecu is also unplugged so its really off 😉
Thus on the days that I witness yo-yo, it only focuses on floating 12.8v and charging up to 14.8 on deceleration / braking
Will continue to observe and report. Has 12.8 ever been achieved from others? I seem to read 12.6 often on mbworld
Trying to replicate the scenario where it would do the typical 12v during driving but so far just 1 driving cycle did that.
Sorry, I missed this question.
For my 200A Valeo alternator, the voltage will be 13.9 to 14.1V at all times, with amperage the one being managed by the alternator.
However, voltage dip will always happen when alternator is hot soaked already, while I am in D mode for tranny and brake HOLD, which is the lowest RPM of 550.....
and then I do rapid and high degree of change on the steering.
Electric power steering is a super big sucker, can be up to 80 amps.
If above condition is at night, that 550 RPM added with headlight load, my alternator can easily be in mild deficit because 550 RPM engine is too low for alternator when already heat soaked
and loaded at 60 amps. Deficit is when the voltage will drop below 13.4V and can be below 12.8V, depending on how much deficit.
At 650 RPM or more, there will be no deficit whatsoever even when heat soaked.
Still observing and reporting but it is still the same situation
Random days I have 14.4v - 14.7 on the entire drive cycle (even with headlights + AC OFF)
Other days it does the yo-yo similar to eco profiles
The only difference is all of my eco parameters are disabled (non functioning button+light) a certain ecu is also unplugged so its really off 😉
Thus on the days that I witness yo-yo, it only focuses on floating 12.8v and charging up to 14.8 on deceleration / braking
Will continue to observe and report. Has 12.8 ever been achieved from others? I seem to read 12.6 often on mbworld
You can get 12.8V while cruising and above 1,000 RPM ? even with ALL-IN disconnected ?
12.8 to 14.9V is NORMAL charge cycle.
12.8V is not 12.6V but it will do just fine to take care of your batteries.
YOYO Territory...
What happens below 12.3V is battery "drain by driving": Periods of deep drain laced with 14.9V bulk 90A high current, short battery life.
composite Osaka blossom - JP.
Last edited by CaliBenzDriver; Nov 6, 2025 at 12:29 AM.
You can get 12.8V while cruising and above 1,000 RPM ? even with ALL-IN disconnected ?
I actually plugged mine back in but yes, on certain drive cycles its 12.8v cruising and idling. 14+ on others (even with No headlights, No AC) 2015 car
I swapped to an alternator with a clutched pulley in hopes to smooth out driveability on shifts (it actually worked!) But I still needed to rev to 1,000 rpm at start for it to start charging (OM651 diesel). Decided to plug it back in as I was getting tired of the car being drained at idle when other people drive the car (4 incidents)
Thus I have decided to plug back in. My experience is positive so far! No longer having issues that I previously had
But will continue to observe and report. Still need to experience DPF Regeneration as well and heat soaking moments. Good thing I have 100 mile commutes
I have a 2010 Mercedes C300 RWD, M272 engine. My car only has one battery, the main one in the engine compartment; there's no auxiliary battery since my car doesn't have Start/Stop. I don't use an AGM battery; it's a conventional Bosch 95Ah, 800 CCA battery, purchased a month ago.
The battery mostly stays at 12.6V, even with the air conditioning and headlights on. Is this normal? It only increases to 14V or more at certain times, such as during braking (engine braking) or when I accelerate hard. I'm unsure because I see that people have discovered a way to keep it always above 14V.
Will what's discussed in this thread work on my Mercedes? Will disconnecting the ALT-LIN cable solve this 12.6V battery problem? Is it safe to do this? If you can help me...
I have a 2010 Mercedes C300 RWD, M272 engine. My car only has one battery, the main one in the engine compartment; there's no auxiliary battery since my car doesn't have Start/Stop. I don't use an AGM battery; it's a conventional Bosch 95Ah, 800 CCA battery, purchased a month ago.
The battery mostly stays at 12.6V, even with the air conditioning and headlights on. Is this normal? It only increases to 14V or more at certain times, such as during braking (engine braking) or when I accelerate hard. I'm unsure because I see that people have discovered a way to keep it always above 14V.
Will what's discussed in this thread work on my Mercedes? Will disconnecting the ALT-LIN cable solve this 12.6V battery problem? Is it safe to do this? If you can help me...
12,6V means that your AltLin is doing the job.The energy management consider that your battery should not be charged ( meaning no fuel spending for nothing).
So where is the problem?
Coasting means free charging.
Always 14V means battery ageing and fuel consumption...is like a loop...you spend more for fuel to get the opportunity to change sooner the battery.
Last edited by trigital; Jan 24, 2026 at 10:08 AM.
12,6V means that your AltLin is doing the job.The energy management consider that your battery should not be charged ( meaning no fuel spending for nothing).
So where is the problem?
Coasting means free charging.
Always 14V means battery ageing and fuel consumption...is like a loop...you spend more for fuel to get the opportunity to change sooner the battery.
Okay! So my car is fine and I don't need to worry?
The topic here talks about always leaving it at 14V, so what's the advantage of that if it wears down the battery? From what I understood on the first page, 12.6V would be bad.
Okay! So my car is fine and I don't need to worry?
The topic here talks about always leaving it at 14V, so what's the advantage of that if it wears down the battery? From what I understood on the first page, 12.6V would be bad.
The topic is about missing "stable" values of the voltage.
If your chasis has "stable" value at 12,6 or 14 or any... means that's everything is OK.
Although...the Start Stop function is not related with AGM/VRLA battery, so I suggest to learn what type of battery is suitable for your car as it seems obvious that you have Energy Management ( blueficeny named in Europe).
The topic is about missing "stable" values of the voltage.
If your chasis has "stable" value at 12,6 or 14 or any... means that's everything is OK.
Although...the Start Stop function is not related with AGM/VRLA battery, so I suggest to learn what type of battery is suitable for your car as it seems obvious that you have Energy Management ( blueficeny named in Europe).
Ah, okay. I'm not in Europe or North America, so it's difficult to fully understand the discussion.
I have a 2010 Mercedes C300 RWD, M272 engine. My car only has one battery, the main one in the engine compartment; there's no auxiliary battery since my car doesn't have Start/Stop. I don't use an AGM battery; it's a conventional Bosch 95Ah, 800 CCA battery, purchased a month ago.
The battery mostly stays at 12.6V, even with the air conditioning and headlights on. Is this normal? It only increases to 14V or more at certain times, such as during braking (engine braking) or when I accelerate hard. I'm unsure because I see that people have discovered a way to keep it always above 14V.
Will what's discussed in this thread work on my Mercedes? Will disconnecting the ALT-LIN cable solve this 12.6V battery problem? Is it safe to do this? If you can help me...
Engine running chassis voltage between 12.6 and 14.9V are normal.
This variable voltage is managed by Bosch ECU and the SAM's to "save gas".
If you never witness battery "drain by driving" below 12.0V & 90Amps... then your advanced voltage control is working.
12.6V only with headlights and/or A/C-On is not correct. Voltage should jump up to 13.7V to carry these higher load current.
The bottom line is battery current should NEVER significantly draining out with engine running.
The experimental "ALT-LIN:OFF" setting is useful to prevent any voltage swings and low battery charge.
Liquid lead-acid electrolyte will release flammable hydrogen when overcharged.
Last edited by CaliBenzDriver; Jan 24, 2026 at 08:28 PM.
12,6V means that your AltLin is doing the job.The energy management consider that your battery should not be charged ( meaning no fuel spending for nothing).
So where is the problem?
Coasting means free charging.
Always 14V means battery ageing and fuel consumption...is like a loop...you spend more for fuel to get the opportunity to change sooner the battery.
Yes, 12.6V is the float voltage that stops battery charge when the battery module is satisfied.
This smart opportunistic charging is the absolute BEST when it works.
Unfortunately this voltage control is not built to be reliable. It is built to disfunction quietly under the radar without any fault.
When CAN-B is disrupted R-SAM is unable to request set voltage from the ECU in charge of ALT-LIN serial link. ECU lets ALT-LIN uncontrolled.
Last edited by CaliBenzDriver; Jan 24, 2026 at 09:39 PM.
Engine running chassis voltage between 12.6 and 14.9V are normal.
This variable voltage is managed by Bosch ECU and the SAM's to "save gas".
If you never witness battery "drain by driving" below 12.0V & 90Amps... then your advanced voltage control is working.
12.6V only with headlights and/or A/C-On is not correct. Voltage should jump up to 13.7V to carry these higher load current.
The bottom line is battery current should NEVER significantly draining out with engine running.
The experimental "ALT-LIN:OFF" setting is useful to prevent any voltage swings and low battery charge.
Liquid lead-acid electrolyte will release flammable hydrogen when overcharged.
My battery (or is it the alternator?) doesn't reach 13.7V even with the air conditioning and lights on; it always stays at 12.6V, except when the car uses engine braking and when I accelerate harder (higher RPMs). Driving at 100 km/h at 1800 RPM (7th gear) with the air conditioning on, it only shows 12.6V. Could it be a problem with the alternator? I had problems with the ABS/ESP module; the voltage dropped significantly, which made me change the battery. My old one was discharged, although the car was running, but the ABS/ESP module was showing errors. After changing the battery and resetting the errors, everything works, but nothing will help if the alternator doesn't properly charge the battery.
In UB mode, it stays at 12.6V most of the time. The IB fluctuates a lot, going from negative to 15A I think. I would have to pay more attention, but it never reaches 90A.
14.1V while at only 100 to 200 milliamps or 0.1 to 0.2 amp is what a good disconnected ALT-LIN alternator will produce when battery already full.
Its like a float voltage of a smart charger.
My battery (or is it the alternator?) doesn't reach 13.7V even with the air conditioning and lights on; it always stays at 12.6V, except when the car uses engine braking and when I accelerate harder (higher RPMs). Driving at 100 km/h at 1800 RPM (7th gear) with the air conditioning on, it only shows 12.6V. Could it be a problem with the alternator? I had problems with the ABS/ESP module; the voltage dropped significantly, which made me change the battery. My old one was discharged, although the car was running, but the ABS/ESP module was showing errors. After changing the battery and resetting the errors, everything works, but nothing will help if the alternator doesn't properly charge the battery.
In UB mode, it stays at 12.6V most of the time. The IB fluctuates a lot, going from negative to 15A I think. I would have to pay more attention, but it never reaches 90A.
So far... your car has no evidence of "drain by driving" - Your battery charge control seems to be responding fairly well from 14.9V all the way to 12.6V.
It's strange that 13.7V voltage is not requested with higher loads.
Try "Headlights:On"... report voltage comes up.
> THEORETICALLY:
Understand the 12.6 Voltage simply powers ALL 100% of consumers without any further charging battery once battery is already charged to satisfaction.
> PRACTICALLY:
-- Pay attention to what happens once the charging system reaches 12.6Volts stage.
-- With this low voltage marginal CAN Bus network modules can go rogue to cause ALT=OFF.
-- Once ALT voltage is no longer controlled by Bosch ECU then "drain by driving" rollercoaster begins. Voltage keeps going lower into 11.0V... no charging system fault code present but many referred errors & Limp-Modes.
Voltage will drain below 12.0V then switch to 14.9V then back to 11.xV then 14.xV then 11.xV then .... this will shoot 90Amp charge into hot drained battery with Zero fault present then back to 11.xV while driving with factory stock setup.
FYI: currently your LIQUID lead-acid battery may be the WRONG battery type installed in a "smart charging" vehicle. Newer AGM batteries GEL type are factory installed to tolerate more abuse without venting explosive hydrogen gas.
> OPERATING RANGES: Above 12.6V is battery charge - NORMAL At 12.6V is battery float ie. no charge - NORMAL Below 12.6V is battery discharge - DANGER
A positive "+15Amp" charging current is within normal range: ok.
A negative "- 40Amp" or greater needs attention - There is no official repairs for this condition ( Not the ECU, ALT, AGM,...).
Last edited by CaliBenzDriver; Jan 26, 2026 at 02:23 PM.
After two weeks without driving the car, I used it again and drove almost 400km in two days. What I noticed the second time I started the car was that the battery went to 14.7V (I think it was that value or something close) for part of the trip (a few minutes) and then dropped to 12.6V. But at some points I noticed 12.4V and 12.5V, which could be quite bad. Is there any explanation for dropping so much while the car is moving, with low beams and the air conditioning on?
I didn't have any problems starting the car or anything; the voltage with the car stopped without the engine running is 12.6V or 12.5V, and when starting it drops to 11.6V and then goes to 14.7V when the engine is running, and the car ran well the entire trip.
After two weeks without driving the car, I used it again and drove almost 400km in two days. What I noticed the second time I started the car was that the battery went to 14.7V (I think it was that value or something close) for part of the trip (a few minutes) and then dropped to 12.6V. But at some points I noticed 12.4V and 12.5V, which could be quite bad. Is there any explanation for dropping so much while the car is moving, with low beams and the air conditioning on?
I didn't have any problems starting the car or anything; the voltage with the car stopped without the engine running is 12.6V or 12.5V, and when starting it drops to 11.6V and then goes to 14.7V when the engine is running, and the car ran well the entire trip.
Anything above 12.6V with engine running is well managed voltage.
What's concerning is battery drained by driving:
12.5 to 11.xVolts.
This drain comes with significant currents involved. Either positive or negative currents with numbers above 15Amps.
High negative discharge or high positive charge are both markers of battery drain.
This may happens after charge cycle enters the 12.6V stage. At that point grumlins wake-up to crash the battery charge logic (network disruption).
Voltages go down lower and currents come up higher.
Do you see that?
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
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