Battery: The Quest for Energy

Hello everyone,

I seem to be having an electrical problem with my 2009 Passat.

In December 2011, I replaced the original battery with a Moll M3 K2 (size 71) and was satisfied with it – although I would have preferred a size 75 if possible.
In October 2012, another battery died, and it was replaced: a new Moll M3 K2 75Ah battery was installed as the starter battery in my car, the old 71Ah battery went into the trunk (for the auxiliary heater), and the old auxiliary heater battery (originally the starter battery from the Passat) was moved to the other car.

Everyone is happy, but now, about 3 months later, the xenon light on the right side is failing again when starting the car. This seems to be a common issue – apparently related to the control unit or something similar.
A few days ago, when I did a quick car scan (for a maximum of 10 minutes!), the radio already reported "Low voltage - I'm going to shut down."

Messgerät sagte mir 12,34V. Wunderte mich extrem, der Wert ist für mich viel zu niedrig. Der Wagen fährt eigentlich jeden Tag - und dann auch keine Kurzstrecke, sondern mind. 30 Minuten. Also Ruhestrom gemessen: 17 - 23mA. AuNo problem.

I plugged the charger into the power outlet overnight and just now (almost exactly 24 hours later!), I unplugged it: The charger is still showing a charging current of 3A (which is the normal charging current)!
The meter reads 12.6V without a charger connected.

So, I connected it, plugged it in, and took out my phone, and then I saw that the voltage was only 12.2V.
When it starts, it looks like this: Video 1 is located here.

After a drive of about 30 minutes, it was parked again: Video 2 is here.


Okay, the all-important question: is it the battery, or what?
The car starts without any problems, so it doesn't sound strained or anything like that when starting. However, I'm not familiar with the voltage dropping so drastically immediately after turning off the engine.


As I mentioned, this item is only 3 months old and has approximately 8,000 km on it.

I've also attached a log of the generator load (it's a bit long, sorry!).


I can't shake this feeling that something is wrong with the device. Could there be other reasons why the battery might have been damaged? Is it possible that something in the generator's control system isn't working correctly? I would have expected the device to initially reach almost 100% before charging the battery...

Should I better take this thing out? I once had a battery that somehow short-circuited during charging – it still showed around 10 volts and was drawing current like crazy...



Thank you for your help.

Marco.

Quote:

I'm not familiar with the phenomenon where the voltage drops so drastically immediately after being turned off.

That was also the "hook" for me.

I would have laughed it off if the operating voltage was 14.3V instead of 14.4V.

What exactly did the "turning off" look like?
Key completely removed?

You've essentially installed everything that can be powered by electricity into your Passat. After you turn off the engine, the ignition... oh wait, it's actually already off. But some control units continue to run for a while.

Generally, mine behaves similarly. The first battery lasted for 4-5 years - I should have replaced it sooner to avoid the last winter. The problem was that it actually ran fine, but when it got extremely cold, nothing would work anymore. It worked perfectly again at 0 degrees Celsius.

Your idle current seems low – are you sure you also detected the voltage spikes?
My cars (especially the 3C models and to some extent the Golf 5) experience power surges every 1-2 seconds, where they draw significantly more current than their baseline level.

And now, my craziest theory:
Do you have many Volkswagen drivers living near you?
I've experienced this phenomenon several times: when visiting certain friends, the car (a Volkswagen Passat) would start poorly when I was leaving.

I wanted to check the quiescent current to see how the Passat reacts when you interact with it using a different VW key fob – of course, it won't unlock immediately, but it needs to first process whether it should or not. If the control unit wakes up and 20 people simultaneously use their key fobs, that could potentially result in a significantly higher energy consumption for your Passat, which might otherwise appear passive.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Hi Martin,

To clarify: I only turned off the engine, I didn't remove the key. This means things like the radio will still be running.
Sure, it still draws a decent amount of power afterward, but after a heavy load, I would expect the voltage to recover back to at least 12.6V.

Dass die Karre realtiv viel Strombedarf hat ist mir schon klar, jedoch läuft der Generator bei ca. 50%, sodass ich mir eine Überforderung bzw. Unterdimensionierung nicht herleiten kann. LAm I doing something wrong?

During the measurement, I observed the twitches you mentioned, which ranged from 17/18 mA to approximately 23/24 mA and occurred periodically, roughly every second.

I like the idea with the remote control, but it's probably other reasons that are more likely to be the cause.
The car is parked on a property in a carport. Within a radius of 200 meters, there are: 3 VWs, 2 Mercedes, 1 Seat, and 1 BMW. They are only unlocked once, and then people drive away - at least, I haven't noticed any neighbors who constantly lock and unlock their cars .



I hope it's just that the battery has become high resistance due to quality defects and that replacing it will solve the problem. When I replace it, I'm considering getting an EFB battery from Moll; there's a very informative thread about them.

I'm going to test my radio power supply again shortly to see if the battery still has any charge left.


Thank you for your reply!

Marco.

Hi Any!

Thank you for the compliments, and congratulations on the good electrician's measuring device .

It initially appears that there is a defect (possibly a short circuit) in the new MOLL battery, as approximately 50 amps should flow from the battery back into the vehicle's onboard electronics immediately after the car is turned off.
It can't be a high resistance either, because that would cause the voltage to drop significantly or completely when starting the engine.

Since it's an open battery, you can remove the vent caps and check the acid levels to see if they are approximately equal. Also, if you have a hydrometer, take some density measurements and record the results.
After that, remove the battery and connect it to a charger at 14.4V for 1-2 days. During this process, the current should drop to a value significantly below 250-500mA and not decrease further.
If the current exceeds 1 or 2 amperes, it indicates a cell short circuit.
Approximately 2 hours after a full charge, perform density measurements again and record the values. This will allow you to reliably assess whether a cell is still functioning or not.

Best regards from Munich!

Hey Bear,

hehe thanks - that was a "bargain" from eBay... The guy didn't have any measuring tapes and didn't know if it worked - €15 immediate purchase .


My hydrometer is probably older than I am, but it consistently shows readings of 1.175 - 1.200 g/cm³.
The acid level in the battery appears to be exactly the same; no deviation can be detected.


I'm going to charge the battery again for another 2 days, as you suggested – let's see if anything happens.

The charging current has now dropped to about 500mA, but my battery charger still shows the same value... The voltage drops relatively quickly to 13V and then slowly decreases.
That looks much better than it did when it was installed.

If the acid concentration doesn't change, I will perform another controlled stress test: I'll add some halogen lights and see what the voltage reads after 1-2 hours.


Thank you for your reply!

Marco.

Hello!

May I ask where you got the battery from?
And furthermore, was it delivered unloaded or already filled?

So, with a density of less than 1.20 kg/L, the battery is essentially almost empty, or has approximately 30% remaining charge.
Normally, it should exhibit a strong demand for electricity and trigger the power supply's current limiting function. Since this isn't happening with you at 500mA, and simultaneously the density is too low in all cells, it can only be that the battery is sulfated.
This happens exclusively when a battery is left uncharged for an extended period of time, and/or there's a problem with the charging regulator/alternator, and/or it has been used primarily for short trips with a high number of electrical consumers running.

Reduce the voltage to 13.8V for a minimum of 2 days to allow desulfation to occur with minimal plate loss. Then, apply 14.4V for another half day, and after a 2-hour break, measure the acid density of all cells again.

The battery will never be new again and is definitely damaged, but it might still be possible to salvage it.

By the way, warranty is excluded in such cases because the issue is not due to a manufacturing defect (MOLL), but rather due to use or storage conditions.
See: http://www.moll-batterien.de/downloads/MOLL_Pruefen_Starterbatterien.pdf

Best regards from Munich!

Hey Bear,

Thank you again for your reply!

Yesterday, I adjusted the voltage at the power supply to 13.9V, which is 13.78 volts above the battery voltage.


The readings from my pH meter seemed strange to me, so I didn't hesitate and spent some time and money today buying a highly precise and scientific hydrometer for €2.99 at the hardware store.

Unfortunately, it's displaying exactly the same thing as my old one did.


Cell -> Previous value (yesterday) -> Current value.
Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.
o 1175 1225
o 1175 1250
o 1175 1250 (approximately)
o 1200 1250
o 1200 1250
o 1175 1225
Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.

Currently, it's charging at 100mA, and it has been doing so since last night.

I find the reported values to be significantly lower than expected, considering that the device consumes almost two days' worth of battery charge. According to the internet, I should have somewhere between 50 and 100 percent battery remaining, but it's much closer to 50% than to 100%.

It's possible I'm being overly cautious: could it be that the acid is somehow "bad," meaning adulterated or "diluted"? The battery was filled and charged. I don't want to say where it came from yet, as I'm still hoping for a warranty claim and an EFB replacement for an additional fee . However, according to the markings on the terminals, the battery wasn't old.

I haven't fully grasped the connection between acid density and charge yet, but I have noticed that my battery isn't reaching the expected acid density even though it indicates a full charge.

A person with no knowledge of the subject might initially think that the problem is simply due to too little sulfuric acid being present.
Can this be corrected?


Best regards,

Marco.

Hey Any!

Yes, it can be corrected: Buy a new battery!

As I explained above, the battery is sulfated.
Generally speaking, one can infer the state of charge from the acid density with much greater accuracy than by measuring the (open-circuit) voltage across the terminals.
1.28 kg/L = 100%; 1.12 kg/L = 0% (at this point, we are already experiencing deep discharge!).
Your battery once discharged to a point where the acid density decreased (as expected), and it either remained in that state for a longer period or was never fully recharged afterward. This caused a structural change in the lead sulfate (not a chemical one!), essentially rendering it "dead" so that it cannot be converted back into lead and acid during a full charge attempt. Consequently, you're experiencing a lack of acid density, even though the battery appears to be nearly full. However, it will never truly be fully charged again because the sulfated layer is no longer reversible, and this part contributes to the current loss of capacity. Additionally, the internal resistance of the cells increases, but this may not be very noticeable in your case since you have a relatively new battery (for now).
Theoretically, you could pour out the acid and replace it with new acid that has a density of 1.28 kg/L. However, this wouldn't help either, because the "dead" material on the plates won't come back to life. So, it would be more work and money for nothing.

I hope I've explained it clearly enough now: the battery is simply dead and will never be "new" again. If the remaining damage is minimal, you can still reinstall the battery and continue using it.
By the way, this kind of capacity loss (whether due to a defect or aging) is usually only noticeable when it reaches around 80-90%!

Let them sit connected to the power supply for a few days, then take another density measurement, and repeat this process for a few more days until the acid density stops increasing.
You can't do much more to revive them , even if you turn yourself upside down trying.

However, one last question remains to be clarified: Did you already purchase a battery that was sulfated (which may not be noticeable during installation and the first start!!) or is your car damaging the battery? Because if it's the latter, even the best EFB battery won't help you in the long run .

Best regards from Munich!

Hi Any!

Is there any update on the revival after almost 2 weeks? *curious*

Best regards from Munich!

Hi there,

Sorry, I completely forgot.


I have finished experimenting with this issue, and even after the "extended charging" process, the acid density did not improve.

In early February, I will meet with the dealer again (I happen to be present), and he wants to test the battery. You've already told me what might come out of that, but I still want someone I can project my anger onto.

Okay, let's put the "Flax" aside for a moment: I've mentally accepted that I have to buy a new battery every 2-3 years – those days of the Golf 2 and 10 years per battery are simply over.



Best regards & thank you for your effort.

Marco.

Hi!

"Sorry, I just happened to come across this topic."
Unfortunately, I can't view the log as a diagram with my old computer; I only see the sequences of numbers.
Am I correct in assuming that the rightmost column represents the onboard voltage?
So, it starts at around just under 12V, then the engine starts and it goes up to about 13.5 - 13.8V?

Hi Any!

If you can't get the battery replaced, then at least use it as a (single-use) alkaline battery, because it's still perfectly capable of doing that.

Otherwise, as still unanswered, be sure to look for any (maintenance/operation/...)-related errors, otherwise you won't be happy in the long run .

Best regards from Munich!

PS: @G.Steffen: ...has actually been circling around the topic for about 20 posts .

DieselBär30x wrote:

PS: @G.Steffen: ...has actually been circling around the topic for about 20 posts

.

Hi D-Bear!

Sure, I understand. I just need an explanation for myself.
I've never created a generator data log like this before.
And since I happened to see this, I thought I'd take a look at it right away.
If I ever have to do this myself.

And that's when I noticed that the (generator voltage? battery voltage? right-hand side) is lower than I would expect.

Steffen G wrote:

And that's when I noticed that the (generator voltage? on-board voltage? right) is lower than I actually expected.

The A/D converters in the ECUs, along with a not very precise diagnostic calibration, actually reduce the reliability of on-board voltage log values towards being rough estimates.

The data is most reliable when used for comparisons, such as to determine the difference between a stationary engine and a charging alternator (LiMA).

If you want to know for sure, use a sufficiently accurate measuring device and measure the voltage directly at the alternator or battery.

Hello Ulf!

Thank you for your reply; it's good to know.
I've always used a good measuring device for that so far.
Then I will continue doing it that way.

Hello everyone!

Behind the scenes, there was a bit more to the initial topic, which, with the originator's permission, I don't want to withhold from you, my diligent readers, in the interest of fairness.

anywhere wrote:

Hi bear =) ... Regarding the bacteria: I've now followed a different lead; I have a feeling it might be the alternator or its control system. "The car had been sitting for two days (which is unusual), and when I started it, both xenon bulbs went out at first (usually only the right one goes out), and it sounded 'a little strained'." Well, I hadn't really thought about anything further, but I knew that something wasn't right. I then drove 10 kilometers and waited for my friends for half an hour, as usual: engine off, parking heater on, music playing, headlights on. After 20 minutes, the system shut down (due to undervoltage - the fan was running at full speed the entire time). Then, after 25 minutes, a message appeared: "You need to start the vehicle now, otherwise I will turn off the radio." After eating, I cycled the 10km back home and checked the voltage with a meter. The voltage was 13.7V at the front and 13.2V at the rear. I initially attributed this to both batteries being discharged, which is why the voltage hadn't reached its "peak" yet. Only then do I start to think more deeply and check my VCDS data. With everything active, the generator load is at 55%, but if I turn off all non-essential consumers, it drops to 45%. Then I took out the charger, and the battery on the back was at "full" after just 2 minutes. The one on the front also started charging quickly; after 3 minutes, it reached 75%, and then I went inside. Currently, everything is still connected. "I just can't figure out what that light machine is doing there!" I understand that the regulator checks the D+ signal to see if the maximum voltage of 14.4V has been reached, and then it reduces the excitation voltage. This causes the voltage to settle somewhere just below 14.4V. If I now see that there are only 13.7 volts above the battery, there can only be two reasons for this: a) The Lima is overheating and can't maintain the voltage because the power draw is too high. b) The regulator is malfunctioning/producing bad results. So, I was searching on Google to see what the typical lifespan of a glow plug is. Apparently, Ford glow plugs can wear out as early as 50,000 kilometers, while Alfa Romeo ones last around 200,000 kilometers, and VW ones have a lifespan of something like 400,000 kilometers. Since I've only downloaded "just" 180k, it's hard for me to imagine, but right now that's kind of the hope I'm clinging to. I can't explain why the voltage is at 13.7V with only a 55% load. There doesn't seem to be any charging electronics or intelligence that would say, "Hmm, let's charge more carefully." Or is this not a feedback loop as I imagine it? Shouldn't the excitation voltage increase until it reaches something around 14.4V – or until 100% load is reached, and the alternator simply can't handle it...? "Tomorrow, Max will give me reference voltages from the various control units so I can check what values I should be seeing. I also found the 13.6V in the engine control unit to be worryingly low; the auxiliary heater showed only 13V." Now I'd like your opinion: Could it actually be the regulator? Or perhaps the brushes or the slip ring? I will call the Bosch service tomorrow () and ask if they have a short time to check it. However, whether the result is useful is something else entirely. I'm really fed up with this topic now - I wish I had just kept my Golf 2... -.- There was never any of this crap back then! Best regards from Munich. marco

As Ulf already mentioned, I wouldn't put too much weight on that. For example, I didn't even look at your log you mentioned earlier, because based on the DMM readings (on the video you still haven't uploaded!!! *exasperated*), it was more than enough for me to rule out a problem with the battery and identify an issue elsewhere.
The reasons why the battery is no longer in good condition have already been explained sufficiently and repeatedly.
Plug the DMM into the cigarette lighter socket and then always enjoy a nice walk together .
The voltages actually measured at the terminals so far would seem to rule out a defect in the alternator/regulator.

Best regards from Munich!