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My Main battery was replaced in 2019 under warranty, too. Regardless, it needs a recharge once a month, as I don't drive it every day.
A recent thread has cleared up confusion regarding the function of both batteries... namely that the Aux battery is primarilly back-up for running accessories while ECO Stop/Start functions (from the main battery). Every time I recharge the main battery, ECO Stop/Start resumes operation with an annoying vengeance. (I've never recharged the Aux Battery, BTW)
I play music in the Comand system all the time, so Comand resumes play everytime I start the engine. I've learned through experience that when Comand fails to turn on when the engine is started, that's my clue that the main battery needs a recharge.
A recent thread has cleared up confusion regarding the function of both batteries... namely that the Aux battery is primarilly back-up for running accessories while ECO Stop/Start functions (from the main battery). Every time I recharge the main battery, ECO Stop/Start resumes operation with an annoying vengeance. (I've never recharged the Aux Battery, BTW).
Absolutely correct. No need to charge the aux battery, if the main battery is fully trickle charged.
anyways, aux battery, after being parked 24 hours, was 12.83V on my Fluke. k, that is good.
popped hood, checked main battery, eeeew. 12.08V ... thats seriously depleted.
Mercedes battery, new in 2019
You are not alone.... It looks like you've got a common case of "Main battery exhibiting low voltage".
It's always a great idea to float-charge lead-acid batteries to minimize plates sulfation. Else the available plate surface gets reduced until capacity calls for replacement.
But batteries are not the subject here, nor is battery drain... UNRELIABLE CHARGE IS a stapple with Benz of this generation across models.
Replacing battery does not prevent further abuse nor fixes the root cause of low charge followed by high discharge (80Amps as displayed while driving in IC).
Fail-safe WORKAROUNDS :
- Driving with your headlights ON pegs alternator output around 13.5V with a guarantee it will not go into discharge (<12.6V) 👍
- Idle out before shutdown when you get to your destination idle out with driver door openedfor 15mn. This will automatically trigger a charge cycle in the 14.5V ballpark. 👍
Upon accelerations alternator is turned OFF for 10 seconds to save fuel. During that time the exhausted battery has to assume the entire car power needs... disruptive glitches 😏
- Keep in mind your vehicle can get into limp mode with a low enough power surge anywhere while driving. Thus it's a real good habit to keep on eye on battery status while driving!
Never mind ECO, ECU or RearSAM...Safety first! I am researching the root cause of uncontrolled discharge.
... Replacing battery does not prevent further abuse nor fixes the root cause of low charge followed by high discharge (80Amps as displayed while driving in IC). ...
"IC" ?
i am tempted to dig out a cigar-outlet voltage monitor we used with our old camper (new one has a bluetooth battery monitoring system), and leaving it plugged into the dash next time I drive around to see how it works. we *do* more short trips than longer ones, maybe every other day, driving errands involving a few miles, stop, a few miles, stop, then home. maybe once a week we go for a longer drive, up or down the coast, or up to the SFBA or Marin (my brothers), driving as much 150 miles. of course, this monitor just measures voltage, not current, as that would require a shunt in series with the battery.
btw, float charge... my main battery charger is a NOCO Genius 10, which does a multi-stage smart charge with peak 10 amps (it scales this to what it thinks the battery needs/wants), a full charge cycle including absorption typically takes 8-12 hours unless the battery is already fully charged.
I have never seen a drain of anywhere close to 80amps in the IC while driving in my 2016. BTW, "IC" is instrument cluster. My car regularly charges at 14.5-14.8v.
Trying to run the headlights to protect a battery is terrible advice. It's much cheaper to replace the battery, plus the cars have DRL and running the lights during the day is just not a good look.
If you need to keep the battery trickle charging, do that. My battery was also replaced in 2019 and is fine. But I drive my car about 1000 miles a month.
i am tempted to dig out a cigar-outlet voltage monitor we used with our old camper (new one has a bluetooth battery monitoring system), and leaving it plugged into the dash next time I drive around to see how it works. we *do* more short trips than longer ones, maybe every other day, driving errands involving a few miles, stop, a few miles, stop, then home. maybe once a week we go for a longer drive, up or down the coast, or up to the SFBA or Marin (my brothers), driving as much 150 miles. of course, this monitor just measures voltage, not current, as that would require a shunt in series with the battery.
IC being the instrument cluster you can set to display the data from the Hyundai Main AGM sensor.
Short trips are fine as the battery charge cycle work fine. The problem is what happens AFTER the charge cycle during longer trips.
As soon as the car ECU is satisfied with battery status it hands over voltage management to RearSAM who is then in charge of modulating running voltage above 12.6V based on Consumers load.
Unfortunately from that point on, things go differently and the smart alternator in parallel with the battery discharges it deeply as if it was a shunt (low voltage, high current load)
disfunctional discharge
Use the shop "service menu" to fisplay batt vitals
How long of a drive is that? I've watched this screen in my car for long drives and have never seen it approach 12.0V except briefly during the startup sequence. It will let it get to 12.4V or so before kicking the engine back on during eco stop/start.
Mercedes batteries (Varta in all of mine) used to last about 7 years or longer. It seems that they don't have the lifespan they used to, but my car's original lasted 4 years and this replacement is a year and a half old now and fine. I can live with that.
I have never seen a drain of anywhere close to 80amps in the IC while driving in my 2016. BTW, "IC" is instrument cluster. My car regularly charges at 14.5-14.8v.
Trying to run the headlights to protect a battery is terrible advice. It's much cheaper to replace the battery, plus the cars have DRL and running the lights during the day is just not a good look.
If you need to keep the battery trickle charging, do that. My battery was also replaced in 2019 and is fine. But I drive my car about 1000 miles a month.
Headlights ON is not for pretty... it's for safety. This requests the ECU to keep voltage above 13.5v and prevents the AGM discharge issues when management goes to la-la-land on highways after charge cycle.
There is no need to fiddle with a charger once you got this yoyo figured out.
40Amp discharge 🤣
Bigger picture is that the AGM battery gets abused with faulty discharge and prematurely wasted. You can float it all day long, the car will complete the normal charge cycle faster then start disfunctional discharge.
Last edited by CaliBenzDriver; 04-24-2021 at 05:06 PM.
Reason: bi
hmm, i'm familiar with the service menu on the COMAND (press the red phone and # buttons for 5 or something seconds?). how do you access the service menu on the instrument panel ?
hmm, i'm familiar with the service menu on the COMAND (press the red phone and # buttons for 5 or something seconds?). how do you access the service menu on the instrument panel ?
It's where you reset oil service flags.
Before engine start, use the steering wheel buttons to call the service menu (see youtube tutorial) then start and drive.
It'll nicely display your battery vitals, very useful on long drives...
How long of a drive is that? I've watched this screen in my car for long drives and have never seen it approach 12.0V except briefly during the startup sequence. It will let it get to 12.4V or so before kicking the engine back on during eco stop/start.
Mercedes batteries (Varta in all of mine) used to last about 7 years or longer. It seems that they don't have the lifespan they used to, but my car's original lasted 4 years and this replacement is a year and a half old now and fine. I can live with that.
It seems that you are blessed with not having that problem. What you describe is textbook perfect the way normal voltages should be.
If you've never seen your battery getting discharged below 12 at highway speed, you're blessed. Typically cruising for over 1hr trips on highways (ie. minimal opportunistic burts of 14.9v)
Where can you buy Varta batteries in the US? I believe these are the OE units rebadged for MB.
Costco does sale our AGM size in stock now (~$180Ea.)
🙂
Last edited by CaliBenzDriver; 04-24-2021 at 05:32 PM.
btw, when I do change my battery, I'm more likely to get a Deka Intimidator AGM than a Mercedes brand batt. I've used East Penn / Deka batteries on a wide range of my cars and not had an issue yet.
btw, when I do change my battery, I'm more likely to get a Deka Intimidator AGM than a Mercedes brand batt. I've used East Penn / Deka batteries on a wide range of my cars and not had an issue yet.
I believe our OEM is short of 1inch in its tray... A wider replacement adds a bit more capacity!
thats the difference between a Group 48/H6 and 49/H9... the 49 batts are typically used in Mercedes diesels, and fit the whole tray, while the 48 is shipped on most gassers, and isn't quite as long and leaves an inch on each end.
Dealer is the only location I know of that sells Varta - at least, the battery says it is Varta. Same with our last vehicle - a Porsche Macan. That car had the original battery and it lasted 6 years even with the smart charging system.
As for your headlights comment, the DRL on these cars more than serves the safety purpose. They are bright and they are very distinctive. No need to run the main beams.
Last edited by LILBENZ230; 04-24-2021 at 06:25 PM.
Dealer is the only location I know of that sells Varta - at least, the battery says it is Varta. Same with our last vehicle - a Porsche Macan. That car had the original battery and it lasted 6 years even with the smart charging system.
As for your headlights comment, the DRL on these cars more than serves the safety purpose. They are bright and they are very distinctive. No need to run the main beams.
Smart charging design is great when it works, a 6 year battery is a good life.
Driving with headlights is only to force the system to deliver above 13.5V (regardless of DRL safety concerns) - I use the word safety because it prevents limp mode at highway speeds from low voltage. (I can give you the test case to reproduce that dangerous failure - Out of scope here 😏
There's a lot of chatter here about trickle charging and stuff but I haven't seen anyone have an issue with low voltage while driving. That would seem to indicate a charging system error, not design.
There's a lot of chatter here about trickle charging and stuff but I haven't seen anyone have an issue with low voltage while driving.
That would seem to indicate a charging system error, not design.
Few people have the finesse to even identify low battery like OP with a long experience.
I am sharing this info to shade light for people who are able to connect the dots about abnormal conditions.
As much as I like my CTEK charger, I am not advocating to simply float batteries.
Instead I have narrowed down the condition that creates low battery charge and premature replacement. No need to recharge these $75k luxury cars anymore 👍
One of these days I will identify the root fix for W212's. As far as I know there is no TSB as of yet. I can write the test case for that as well ("post charge cycle disfunctional AGM discharge"). Not my fun.
Other people with similar experience may shine more light on the cause. The dealer and my master indy could not pin a solution... so I am forced to make lemonade.
😃
Last edited by CaliBenzDriver; 04-24-2021 at 08:06 PM.
Dealer is the only location I know of that sells Varta - at least, the battery says it is Varta. Same with our last vehicle - a Porsche Macan. That car had the original battery and it lasted 6 years even with the smart charging system.
As for your headlights comment, the DRL on these cars more than serves the safety purpose. They are bright and they are very distinctive. No need to run the main beams.
Varta is made by JCI/Clarios. You can get a Champion battery from Pepboys that is also made by JCI/Clarios. Autozone and Advance Auto also carry the same AGM battery, but Pepboys has a 48 month warranty and Autozone/Adance Auto is only a 3 year warranty. My battery is the original OEM one at 10 years old now and the one in my W211 is also oem at 13+ years. The original date is on stamped on the post, has a week and year date code on it. I just use a cheap Schumacher 8amp charger for my battery. Only had to use it a couple times, once when I left the fog lights on and another time when it died on a super cold day. I might have been sitting in the car too much listening to the radio or talking on the phone after the car is off at night where it leaves the lights on until you get out. Inflation is real, bought this charger for around $25 a few years ago.
Nothing wrong with your car. 12.0V is fine. A healthy late model car will start with 10.5 (ask me how I know). Other than cycle life, resting SOC isn't a big deal (other than being a potential indicator to it's lifespan), your alt does all the work while the engine is running.
AGM SOC
I am having a tough time following this logic..."12.0v is fine and 10.5 starts a car" : your diagram shows 0% charged - how does that work?
Where you're a bit mistaken is: "your alt does all the work while the engine is running" - Nop not during accelerations when alt is OFF and AGM supplies 100% of consumers during the acceleration phase.
This is why I made a few recommendations above to prevent going Limp-mode at freeway/highway/autobahn speeds when exhausted battery shorts out... SOS.
😏
so, just got home from driving around town, mostly low speed cruise. I should note, I live a mile up a 6-8% grade. less than an hour after getting home, I measured the main battery at 12.35, not as bad as the 12.08 of the other day but still down in the weeds.
so, just got home from driving around town, mostly low speed cruise. I should note, I live a mile up a 6-8% grade. less than an hour after getting home, I measured the main battery at 12.35, not as bad as the 12.08 of the other day but still down in the weeds.
so I stuck my NOCO Genius 10 on it, in AGM mode.
Why is your battery voltage still low after driving?
04-24-2021, 05:49 AM
