Battery level is fluctuated when turning on auto start stop
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Gle 400d v167 2019
Battery level is fluctuated when turning on auto start stop
In the MBUX screen under Info > Engine, you can monitor the battery voltage. While the car is running with auto start-stop enabled, I observe the voltage fluctuating between 12.5V and 14.8V. However, when I disable the start-stop feature, the voltage remains stable at 14.7V.
I'm curious about why this happens. I think that when the car is running, the alternator is functioning as well. It seems the auto start-stop system may disconnect the alternator or halt battery charging to assess the battery voltage for stopping the engine. During this time, the voltage fluctuates between the battery's voltage and the alternator's output. This could mean that the start-stop function results in less efficient battery charging and may negatively impact the battery due to frequent short charges. I do not know if AGM battery like short charge or not.
Please correct me if I am wrong.
I'm curious about why this happens. I think that when the car is running, the alternator is functioning as well. It seems the auto start-stop system may disconnect the alternator or halt battery charging to assess the battery voltage for stopping the engine. During this time, the voltage fluctuates between the battery's voltage and the alternator's output. This could mean that the start-stop function results in less efficient battery charging and may negatively impact the battery due to frequent short charges. I do not know if AGM battery like short charge or not.
Please correct me if I am wrong.
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When the battery is being charged by the alternator, ~14.5 volts is normal. When start/stop is being used, the alternator isn't operating in the stop mode, and normal battery voltage ~12.5 volts is present.
The topic is controversial, but IMO start/stop accelerates the wear on the battery and starter. Mostly, I just find the feature annoying and of no fuel efficiency benefit to me, so I've permanently disabled it.
The topic is controversial, but IMO start/stop accelerates the wear on the battery and starter. Mostly, I just find the feature annoying and of no fuel efficiency benefit to me, so I've permanently disabled it.
Last edited by streborx; Oct 19, 2024 at 09:33 AM.
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2021 GLS580 | 2011 ML350 BlueTec | 2009 Pontiac G8 GXP
12.4v is considered fully charged for a resting 12v battery. When running the alternator provides ~14.4 - 14.8v to charge. That's perfectly normal and expected.
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From: Maryland
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
I have disabled the Start/Stop feature permanently. If you search, you will find that Start/Stop is not beneficial to the engine or transmission, but only provided by the manufacturer to help meet fleet mileage mandates. Since virtually all new cars have it, it is more of a novelty for the uninformed. Do your engine and transmission a favor and disable it. The fuel savings are negligible compared to the cost of the wear and tear on the engine. As long as the engine is running, there is a film of oil protecting all moving parts. Engine off and that oil film starts draining into the sump. The constant stopping and starting multiplies the amount of wear on the crank shaft, bearings, cam shaft, guides, etc.
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I have disabled the Start/Stop feature permanently. If you search, you will find that Start/Stop is not beneficial to the engine or transmission, but only provided by the manufacturer to help meet fleet mileage mandates. Since virtually all new cars have it, it is more of a novelty for the uninformed. Do your engine and transmission a favor and disable it. The fuel savings are negligible compared to the cost of the wear and tear on the engine. As long as the engine is running, there is a film of oil protecting all moving parts. Engine off and that oil film starts draining into the sump. The constant stopping and starting multiplies the amount of wear on the crank shaft, bearings, cam shaft, guides, etc.
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From: Maryland
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
There are a couple of ways. You can't do it from XENTRY but need to use one of the other programming tools. I don't know how to do it, but @BenzNinja can do it such that it remembers the last setting, either on or off. In my case, before I became familiar with BenzNinja, I purchased two dongles from Mid City Engineering to do the same. I have two cars, so my expense was doubled. I could have put that money toward a BenzNinja Club membership or SDS components if I had known.
The dongles worked, but they were essentially single use, whereas the BenzNinja Club membership has been immensely more valuable.
The dongles worked, but they were essentially single use, whereas the BenzNinja Club membership has been immensely more valuable.
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There are a couple of forum threads on how to disable start/stop, among them:
https://mbworld.org/forums/e-class-w...ii-reader.html describes how to do it with the Launch OBD scanner.
https://mbworld.org/forums/mercedes-...o-dummies.html describes how to do it with Xentry.
I used the Launch scanner method, but prior to that drove for several months with the battery charging sensor disconnected (effective, but admittedly a hack).
Further to the OP's inquiry, there are a variety of parameters that enable or suspend the start/stop function. One is the charge state of the starter battery. There's a current sensor (the one I disconnected) attached to the battery's negative terminal that measures charging current. If the alternator is applying a substantial charge current to the battery -- for instance, after many start/stop cycles in bumper to bumper traffic on the LA freeway -- start/stop is suspended so that the car doesn't stop and then have insufficient battery capacity to start.
JettaRed's comments above are correct -- start/stop scores fuel economy points for manufacturers and is not beneficial to the majority of drivers.
https://mbworld.org/forums/e-class-w...ii-reader.html describes how to do it with the Launch OBD scanner.
https://mbworld.org/forums/mercedes-...o-dummies.html describes how to do it with Xentry.
I used the Launch scanner method, but prior to that drove for several months with the battery charging sensor disconnected (effective, but admittedly a hack).
Further to the OP's inquiry, there are a variety of parameters that enable or suspend the start/stop function. One is the charge state of the starter battery. There's a current sensor (the one I disconnected) attached to the battery's negative terminal that measures charging current. If the alternator is applying a substantial charge current to the battery -- for instance, after many start/stop cycles in bumper to bumper traffic on the LA freeway -- start/stop is suspended so that the car doesn't stop and then have insufficient battery capacity to start.
JettaRed's comments above are correct -- start/stop scores fuel economy points for manufacturers and is not beneficial to the majority of drivers.
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There are a couple of forum threads on how to disable start/stop, among them:
https://mbworld.org/forums/e-class-w...ii-reader.html describes how to do it with the Launch OBD scanner.
https://mbworld.org/forums/mercedes-...o-dummies.html describes how to do it with Xentry.
I used the Launch scanner method, but prior to that drove for several months with the battery charging sensor disconnected (effective, but admittedly a hack).
Further to the OP's inquiry, there are a variety of parameters that enable or suspend the start/stop function. One is the charge state of the starter battery. There's a current sensor (the one I disconnected) attached to the battery's negative terminal that measures charging current. If the alternator is applying a substantial charge current to the battery -- for instance, after many start/stop cycles in bumper to bumper traffic on the LA freeway -- start/stop is suspended so that the car doesn't stop and then have insufficient battery capacity to start.
JettaRed's comments above are correct -- start/stop scores fuel economy points for manufacturers and is not beneficial to the majority of drivers.
https://mbworld.org/forums/e-class-w...ii-reader.html describes how to do it with the Launch OBD scanner.
https://mbworld.org/forums/mercedes-...o-dummies.html describes how to do it with Xentry.
I used the Launch scanner method, but prior to that drove for several months with the battery charging sensor disconnected (effective, but admittedly a hack).
Further to the OP's inquiry, there are a variety of parameters that enable or suspend the start/stop function. One is the charge state of the starter battery. There's a current sensor (the one I disconnected) attached to the battery's negative terminal that measures charging current. If the alternator is applying a substantial charge current to the battery -- for instance, after many start/stop cycles in bumper to bumper traffic on the LA freeway -- start/stop is suspended so that the car doesn't stop and then have insufficient battery capacity to start.
JettaRed's comments above are correct -- start/stop scores fuel economy points for manufacturers and is not beneficial to the majority of drivers.
Then there is also this, unplugging the battery sensor, don't recommend it because the car checks the voltage real time with this sensor so if unplugging it, the alternator will run at full all the time and also RPMs at idle will be slightly higher:
https://mbworld.org/forums/c-class-w...tart-stop.html
https://mbworld.org/forums/c-class-w...ngle-plug.html
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From: Colorado
'21 AMG53 wDPP & ARC, 19 GLC300 - Former-03 C240,2 ML BlueTecs,20 GLE450 E-ABC,15 Cayenne D,17 Macan
I have disabled the Start/Stop feature permanently. If you search, you will find that Start/Stop is not beneficial to the engine or transmission, but only provided by the manufacturer to help meet fleet mileage mandates. Since virtually all new cars have it, it is more of a novelty for the uninformed. Do your engine and transmission a favor and disable it. The fuel savings are negligible compared to the cost of the wear and tear on the engine. As long as the engine is running, there is a film of oil protecting all moving parts. Engine off and that oil film starts draining into the sump. The constant stopping and starting multiplies the amount of wear on the crank shaft, bearings, cam shaft, guides, etc.
Fuel savings can actually be significant. They definitely are significant on the EPA test cycle, which is why manufacturers use it.
Start/stop with an ISG doesn't involve any gears, and the tranny doesn't see any stress because it's not involved.
Motor oil's film strength has improved, and interior tolerances are tighter, so there is less drainback and therefore the wear issue is reduced on engines specifying 0WXX or 5WXX. So it's less of an issue than ones specifying 15WXX or 20WXX. Days gone by.
I haven't seen any current data on newer engines that show results similar to decade-old data that shows 5-30% increased wear due to drainback. Have you?
The only thing that's clear from a variety of forums, is that Start /Stop is generally despised (mostley by non-ISG owners).
And that several folks have paid to disable it.
I seldom keep modern cars over 100k miles, so their potential reduction in engine life from 280,000 miles to 220,000 miles isn't an issue for me. I'd add zinc additives if I wanted to be kinder to my bearings.
Plus, my passengers can't tell me when it Starts or Stops. If it were obtrusive, I might be more concerned.
It's a personal preference.
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https://mbworld.org/forums/s-class-w...tart-stop.html
Then there is also this, unplugging the battery sensor, don't recommend it because the car checks the voltage real time with this sensor so if unplugging it, the alternator will run at full all the time and also RPMs at idle will be slightly higher:
https://mbworld.org/forums/c-class-w...tart-stop.html
https://mbworld.org/forums/c-class-w...ngle-plug.html
Then there is also this, unplugging the battery sensor, don't recommend it because the car checks the voltage real time with this sensor so if unplugging it, the alternator will run at full all the time and also RPMs at idle will be slightly higher:
https://mbworld.org/forums/c-class-w...tart-stop.html
https://mbworld.org/forums/c-class-w...ngle-plug.html
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From: Maryland
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
One of the primary reasons I disabled mine was, prior to knowing the potential for extra wear, was my wife absolutely hated it and asked if something could be done. For a car guy like me, that was being given $5 and let loose in the penny candy store. I always had a nagging fear that the car wouldn't start and be ready to immediately go when pulling out into heavy traffic from a side street. But, as you said, it's a personal preference.
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2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
@JettaRed what's your car? With or without ISG?
2014 C350
2015 SL400
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@JettaRed what's your car? With or without ISG?
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Vehicles with ISG are smoother for sure when it comes to start/stop due to the design of it. By the way, saw this video, talks about hybrids but not just mild-hybrids, cool to see the engineering behind it: https://www.youtube.com/watch?v=3eC5FFoCq4s
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I admit I haven't watched the video yet but his videos were usually legit, since it just showed up in my subscriptions I thought I would share it as it corresponds with the topic being discussed. If I do watch it and turns out in a way of how you described it, that would be disappointing.
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For me, the smoother start/stop performance of an ISG equipped vehicle is not worth the consequences of mild hybrid malfunctioning. Mild hybrid systems are entirely nonessential to the propulsion of the vehicle under conventional ICE power, yet are designed to cripple the car immediately when/if anything goes amiss, or even becomes indeterminant. This is a safety issue, not a fuel efficiency issue. An ISG/mild hybrid equipped vehicle should at least allow a driveable range and/or time before bricking it. Maybe only 1% of ISG vehicles experience problems, but IMO that's 1% too many.
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He's pretty reliable at that, so he gets plenty of invites. He is either not aware of others who provide the same or better services /features, or hides that info.
He makes his diagrams overly complicated so they're difficult to understand. Plus in many cases they're just wrong.
I quit watching him about 2 years ago.
He's in my Scotty Kilmer category.
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For me, the smoother start/stop performance of an ISG equipped vehicle is not worth the consequences of mild hybrid malfunctioning. Mild hybrid systems are entirely nonessential to the propulsion of the vehicle under conventional ICE power, yet are designed to cripple the car immediately when/if anything goes amiss, or even becomes indeterminant. This is a safety issue, not a fuel efficiency issue. An ISG/mild hybrid equipped vehicle should at least allow a driveable range and/or time before bricking it. Maybe only 1% of ISG vehicles experience problems, but IMO that's 1% too many.
MBWorld Fanatic!
Joined: Oct 2009
Posts: 6,989
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From: Colorado
'21 AMG53 wDPP & ARC, 19 GLC300 - Former-03 C240,2 ML BlueTecs,20 GLE450 E-ABC,15 Cayenne D,17 Macan
For me, the smoother start/stop performance of an ISG equipped vehicle is not worth the consequences of mild hybrid malfunctioning. Mild hybrid systems are entirely nonessential to the propulsion of the vehicle under conventional ICE power, yet are designed to cripple the car immediately when/if anything goes amiss, or even becomes indeterminant. This is a safety issue, not a fuel efficiency issue. An ISG/mild hybrid equipped vehicle should at least allow a driveable range and/or time before bricking it. Maybe only 1% of ISG vehicles experience problems, but IMO that's 1% too many.
The ISG provides an entirely different set of advantages.
It provides a 48v system that eliminates belt-driven accessories such as water pump, AC compressor, and suspensions. It also gives immediate throttle response by adding 180 lb-ft of torque, and regenerative braking that saves brake wear
I don't remember any complaints about a failed ISG on the forum.
It makes the car feel like a naturally aspirated car.
And an almost imperceptible start / stop feature.
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I think we have a nomenclature problem here. A mild hybrid does not provide electric-only driving. None do.
The ISG provides an entirely different set of advantages.
It provides a 48v system that eliminates belt-driven accessories such as water pump, AC compressor, and suspensions. It also gives immediate throttle response by adding 180 lb-ft of torque, and regenerative braking that saves brake wear
I don't remember any complaints about a failed ISG on the forum.
It makes the car feel like a naturally aspirated car.
And an almost imperceptible start / stop feature.
The ISG provides an entirely different set of advantages.
It provides a 48v system that eliminates belt-driven accessories such as water pump, AC compressor, and suspensions. It also gives immediate throttle response by adding 180 lb-ft of torque, and regenerative braking that saves brake wear
I don't remember any complaints about a failed ISG on the forum.
It makes the car feel like a naturally aspirated car.
And an almost imperceptible start / stop feature.
MBWorld God!
Joined: Dec 2019
Posts: 32,231
Likes: 6,285
I think we have a nomenclature problem here. A mild hybrid does not provide electric-only driving. None do.
The ISG provides an entirely different set of advantages.
It provides a 48v system that eliminates belt-driven accessories such as water pump, AC compressor, and suspensions. It also gives immediate throttle response by adding 180 lb-ft of torque, and regenerative braking that saves brake wear
I don't remember any complaints about a failed ISG on the forum.
It makes the car feel like a naturally aspirated car.
And an almost imperceptible start / stop feature.
The ISG provides an entirely different set of advantages.
It provides a 48v system that eliminates belt-driven accessories such as water pump, AC compressor, and suspensions. It also gives immediate throttle response by adding 180 lb-ft of torque, and regenerative braking that saves brake wear
I don't remember any complaints about a failed ISG on the forum.
It makes the car feel like a naturally aspirated car.
And an almost imperceptible start / stop feature.
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From: Columbus, GA
'25 MB GLE 450, w/airmatic
I think we have a nomenclature problem here. A mild hybrid does not provide electric-only driving. None do.
The ISG provides an entirely different set of advantages.
It provides a 48v system that eliminates belt-driven accessories such as water pump, AC compressor, and suspensions. It also gives immediate throttle response by adding 180 lb-ft of torque, and regenerative braking that saves brake wear
I don't remember any complaints about a failed ISG on the forum.
It makes the car feel like a naturally aspirated car.
And an almost imperceptible start / stop feature.
The ISG provides an entirely different set of advantages.
It provides a 48v system that eliminates belt-driven accessories such as water pump, AC compressor, and suspensions. It also gives immediate throttle response by adding 180 lb-ft of torque, and regenerative braking that saves brake wear
I don't remember any complaints about a failed ISG on the forum.
It makes the car feel like a naturally aspirated car.
And an almost imperceptible start / stop feature.
