My 2011's battery keeps losing power over several days to a week after a charge to where it doesn't have enough juice to start.
Looking at the voltage menu on the dash, it looks like it isn't charging enough the amps are negative for the most part, unless I am in reverse.
I replaced the alternator and it didn't change much.
Any ideas are appreciated

 

Would you mind taking a picture of the battery connections? In particular the positive side. we would like to see if you have the Valeo device at it.

Also, unrelated to the current issue. The fuel pumps in these cars are cooled by the fuel in the tank, which is submerged cooling. Try to keep your tank above the level that triggers the light on the dash, say @1/4 tank.

 

perfect float condition: 12.6V neutral battery current 👍

What you describe is a slow battery drain while parked, right?
You hands on testing shows it's Not the type of drain where ECU gone-wild drains near 12.0V while driving.

This excellent defect issue is built-in the F-SAM power manager. While the chassis is sleeping, it has a wake up timer to query other peripherals then re-enters the low power mode.

The drain issue is centered around how long those wake-up cycles last. Disrupted modules cause F-SAM to stay awake longer than it should. When the network is slow, everything sufers latencies including the ECU timings.

Mercedes has developed a SW tool for sleep-study but regardless keeps manufacturing the same offenders : amazing EIS module, one of the bad guys here.
Other causes can compete to slow down the sleep timer... scan you chassis for codes to give us complete list of faults.

1-- To work around that condition, simply use a CTEK float charger to keep up your battery condition.

2-- Low-voltage conditions drive LIN networked modules crazy. To temporarily relief that, you want to indulge in scanner resets plus reboot power cycles including AUX. Luckily AUX batt is not subjet to drain itself but does provide power when Main is disconnected.

 

Normality i full it up when it gets no lower than 1/4 tank

 

So, the battery does drain, but not when sitting around. I've been out of town for a month and, if it was charged a few days before i had left, the battery still starts the car. The problem is more that if i dont treat my car as a Tesla (my wife's joke about it) and plug it in every 2-3 days. I risk the embarrassment to have to jump it in public.
I don't remember doing that when I first bought it.
I checked for parasitic drains, and after 5-10 min, the negative load fell below 0.03A

 

@CaliBenzDriver , these two pictures worry me a bit. Lights are ON, and system is discharging at idle.

we have concluded that with full load, the system will default to full charging at 14.x V.

I understand the car is draining during use, not standing. Valeo controller out of whack?

How do we force the system to failsafe, i.e., not ECO mode? Just charge until battery is full.

 

Let's keep ECO out of "battery drain while parked". ECO gets disabled when ECU is no satisfied with battery status: charge level or internal resistance condition.

I think you're right about missing 13.7V under load. OP is showing pics with HL=ON and ECU/R-SAM is still commanding a float voltage which it should not... - That's a hint something odd may be going on.


The smart Valeo regulator is used in dumb mode by Mercedes. It is remotely controlled to makes no decision and to deliver voltage ordered by ECU through LIN bus. I am 99% sure OP's regulator is fine.
Instead of having ALT measure voltage internally, ECU uses a sensor bolted on the battery - This provides compensation for voltage dropped along the way to batt.



perfect charging voltage steps controlled by ECU


Voltage stuck on float regardless of HL Load....!

> The "12.5V -2.3A":
this happens normally when switching electric loads on. The ECU purposely marks a quick pause before slowly ramping voltage to offset wiring losses to supply the load demand.

Trouble is when you see 12.3V or less while driving (never mind 12.1V before starting).
Observe voltage slowly ramping up after starting. You should not see any voltage jumps up/down, only controlled ramps to prevent current spikes.


None of that deals with OP "drain while parked". MB is hanging to that struggle like a trademark feature or the accelerator pedal requiring investigation...

The strategy to deal with that drama is multi-fold:
- Float Main batt as needed.
- Undo the solderless game.
That's what I wrote to help in my prior answer.

The outcome is a chassis that does not eat batteries. When voltage drops below AUX it steps up through its relay and gets wasted to helpout the Main.


+++ Hope all our Floridian friends stay safe during hurricane Idalia +++

 

Do you think that this is normal charging? I would think that after driving, the battery should be charged, and most of the time it is not

 

Yes, I think your Main batt is well charged to the point ECU decides to enter float mode ie. 12.6V with low amps.

You are definitely NOT a recipient of the "yo-yo voltage" chaos.
Your alternator supplies your 25Amp consumers at all time. If not IC would read high current in the thirties. Your display is not showing us that, right?


Battery sensor data displayed by IC. shows excellent low charge currents is. Main is nearly full.I don't quite understand what makes you think battery is not charged well ?

12.6V is the maintenance float voltage applied after charge is completed. That satisfies ECU criterias.

100% of the car power is supplied by alternator - Main battery power is only used to crank starter, not for driving needs when it acts as a large power capacitor.

A 12Volts lead acid battery voltage is not 14.4, that is only bulk charging voltage.

12.6V is great stage to reach!
As discussed earlier, I understand your issue is with "drain while parked" to feed sleepless vempires.

A system reboot will resume good behaviors in addition to CTEK float (Do not AGM settings with battery connected to MB!)

 

My main issue is that unless I have charged the battery recently the car wouldn't start. This makes me think that the battery isn't charged enough. I considered that the starter might be getting tired, but when I watch the voltage, it drops to 9v, while cranking.
Thanks for your help

 

Dess, if you are a member of Sams Club, you can ask them to load test your battery. They use Midtronics battery testers (the same MB uses at dealerships), and measure the health of your main battery. I am not certain if your model uses the small or the medium size auxiliary battery. Do you have a second battery in the trunk? If not, your car uses the small battery on the driver's side behind the dash.

A normal/good condition battery should not drop the voltage that much when cranking an engine in good condition. If the battery is good health, and there is that much voltage drop during cranking there may be a resistance problem between the battery and the starter. One of the weak links is the ground strap from the engine to the body, sometimes called the WTF ground point.

Once we are clear the battery is in good health, we can start isolating the next possible issue. @CaliBenzDriver already blessed the voltage regulator/alternator; therefore, either you drive too short trips for the main to recharge, or you have a drain when the car is parked (which @CaliBenzDriver highlighted already).

 

There are no Sams clubs left in my town (Rochester, NY). Who else would have that tester?
I have the small auxiliary battery in the dash. Replaced it last week, just in case (even though I never had an error message).
Even after an 8 hour drive, if I park the car for an hour or so and I go in and out of it (not allow it to sleep) a few times, it might not start or it would struggle. In contrast, after it's been on the charger all night, I can go in and out of it for hours (for a few days) and the battery would still be "fully charged" spinning that starter like a good pizza maker spins dough. This makes me think that the battery isn't being charged enough by the alternator. Am I wrong?

 

AA. How long after engine shut down is this wait of 5-10 minutes you speak of ?
If you are after a trip, even a short trip, the modules Deep Sleep will not occur as fast as in10 minutes. Can be up to 2 hours later a Deep Sleep will then occur.
I asked this because if you read 30 milliamps only, after engine kill and wait for 10 minutes only, the milliamps value must be wrong.

Deep Sleep will occur fast like in 10-15 minutes only if your engine been shut down many many hours ago , like up to 6 hours ago for my car and I keep the hood open right after engine kill so that
testing will not wake up modules by door openings. When I killed engine for 12+ hours ago and entire the car is at ambient temperature already, even if modules woke up, it will go to deep sleep
within 12 minutes if I open the door. See below :


While our engine is different, it is ECM MED177 family, I would assume Deep Sleep protocol would be the same.

BB. I suppose the 30 milliamps you measured is using DMM and not current clamp, right ?

CC. How old is your battery ?

 

I have seen it as well in some BatteryPlus stores. The AutoZone close to me uses something else, but worth a try. The battery health is not the same as the battery voltage when charged. A bad battery can be charged up to 12.6V, and not be able to crank a toy since the CCA (Cold Crank Amperage) available may be too low --> effectively dead.

 

Q: Have you charged your battery directly connected to it?
If so the battery sensor could not register charge properly and needs a reboot.


battery sensor keeps the tally of charge


Smart LIN sensor

-- Do charge by connecting to the grounding stud on chassis to keep the battery sensor aware of charge.

-- Do not connect directly to battery posts for that matter.

Hyundai sensor is a shunt that measures and computes battery charge.

 

Walmart and they're everywhere.

 

Walmart SuperCenter with Tire Center

None of the 3 closest Walmarts around me have a service center. Just auto products and nobody is knowledgeable enough to help you

 

I was looking at batt to read the date code when I spotted something that may help solve this enigma... the NEG POS cable is not inserted well for a good connection... high drop voltage under cranking load ✌️


here is your date code 🙂


POSITIVE NEGATIVE side is well inserted deep down the batt post


NEGATIVE POSITIVE side is just seating on top of batt post !!! 😳

This has a pretty good chance to help get you normal power.
The battery post has a cone shape so does the connector... this is a 700Amp connection: a little resistance can really drop significant voltage.

Good day?
🤞

 

and if you are visiting a fully featured Walmart for the load test, do not forget
1 - https://www.walmart.com/ip/Hyper-Tou...7?from=/search, and clean both posts.
2 - https://www.walmart.com/ip/CTEK-40-2...4?from=/search -> if you decide for the battery maintainer anyway. I have that one in particular (from Amazon, circa 2021)

 

I measured it using a multi voltage meter connecting to negative terminal and to clamp. I measured it when the car had been sitting for a while (with the engine shut off) after I started the engine for a minute, not aware that it matters how long it's driven.
When you disconnect the negative to connect the tester, doesn't that wake the modules up?

 

Most likely from removing it several times to connect the miltimeter to chech for parasitic draw. I will make sure it's inserted to the bottom, however, battery was crapping out long before I took it off for a first time.

 

Ok I see...so long you know.

Apologies, I've screwed up polarities side !!
The loose side is POS
The Hyundai sensor is NEG

(The facelift cars have a contraption over the POS side that in your case is hosted inside the Prefuse box)

To summarize: we are now aiming towards a bad battery cell.
👍

 

Here is a nice instructive video about battery, charging system and battery drains

 

I think you had it right the first time. Pretty sure the one witht he "sensor" is the positive.

 

Are you suggesting I buy a new battery? It is a few years old, but I replaced it because it was doing the same thing with the old one. Didn't improve much (maybe lasted a little longer between the need to recharge). After the battery, I replaced the voltage regulator in the original alternator, after it didn't fix the issue, I (2-3 years ago) replaced the alternator (with a used one from a very low mileage car). That iproved the situation, but never fixed it completely. This week i replaced the voltage regulator of this alternator and didnt fix the problem. If you think the battery should be replaced, I'll do it.