[Tracshan]

Does BMW vehicles measure battery amperage / capacity during registration or any other time for that matter?

If yes, how is this done / determined, is it simply using voltage to determine?

92 Ah at 12.5v would suggest a full battery, also 105 Ah at 12.5v would suggest a full battery, both are different capacity but would somewhat be considered fully charged.

Can BMW vehicle tell the difference between 92 Ah and 105 Ah ?

Amperage is usually measured with load drawn, i am wondering if it somehow monitors the voltage drop with load over time to determine capacity.

[Raimo5]

If you are asking whether IBS with BPM/APM is capable of determining nominal capacity of battery, then no. That is why you need to enter the capacity during registration. Only way for car to ascertain actual capacity is to charge it completely full and then let it drain completely empty. Obviously, you don't want that to happen, and system is designed not to let it happen.

Once you have fed correct data to power management system during registration, IBS will start monitoring current draw, both during operation and rest, voltage dips across all operating conditions and can very accurately determine the battery State of Charge and state of health.

If battery replacement is left unregistered, especially with different type and capacity of batteries, you might end up with power management errors because battery voltage does not correspond to what it should be with the current fed or taken out of it.

[Tracshan]

If you are asking whether IBS with BPM/APM is capable of determining nominal capacity of battery, then no. That is why you need to enter the capacity during registration. Only way for car to ascertain actual capacity is to charge it completely full and then let it drain completely empty. Obviously, you don't want that to happen, and system is designed not to let it happen.

Once you have fed correct data to power management system during registration, IBS will start monitoring current draw, both during operation and rest, voltage dips across all operating conditions and can very accurately determine the battery State of Charge and state of health.

If battery replacement is left unregistered, especially with different type and capacity of batteries, you might end up with power management errors because battery voltage does not correspond to what it should be with the current fed or taken out of it.

@Raimo5, thanks for taking the time to share this information. 

Yes I was referring to IBS. So basically if incorrect information is fed during registration,  the determination will be made using that incorrect information, no real way of the system knowing / verifying. 

Based on my understanding with the relationship between voltage and amperage, going forward after registration, state of Charge will be determined based on voltage drop along with the information fed during registration.

[Node]

Have NO idea what voltage drop you refer to. IBS constantly monitors energy into vs energy out from battery. Because ALL it can measure is voltage, current and temperature (hence recommendation to NOT charge battery via it's terminals, but via a point under the hood, as IBS can't calculate that then). Data is fed into DME/DDE which then calculates battery state taking into account battery voltage, age and temperature too.

If car is of newer model (like G+ series, maybe some Fs) then DME/DDE will also regulate charging voltage based on battery age, temperature, calculated charge level and registered type.

[Tracshan]

Have NO idea what voltage drop you refer to. IBS constantly monitors energy into vs energy out from battery. Because ALL it can measure is voltage, current and temperature (hence recommendation to NOT charge battery via it's terminals, but via a point under the hood, as IBS can't calculate that then). Data is fed into DME/DDE which then calculates battery state taking into account battery voltage, age and temperature too.

If car is of newer model (like G+ series, maybe some Fs) then DME/DDE will also regulate charging voltage based on battery age, temperature, calculated charge level and registered type.

@Node thanks for sharing that information.  Voltage drop I refer to is in general about batteries, once a battery capacity starts reducing, the voltage starts to drop. A dead 12v battery will not measure 12.5v for sure. So I was wondering initially, if IBS does its monitoring along with whichever other module or modules doing calculations based on the battery voltage along with information fed during registration to determine state of Charge.


The main thing I am trying to figure is if the vehicle can know that the incorrect battery is installed without feeding it that information. For example, the vehicle requires 105 Ah and 92 Ah is installed. Can the vehicle recognize this in a fully charged battery and start shutting down modules?

[Node]

I think you are VERY confused about 12.5V. That is not a fixed number and depends on various things (temperature, load, etc). Of course, we are talking lead-acid chemistry here.

That said you can easily charge 12V car battery to 20V. Just connect it to that voltage and leave for a day or two. Of course, there will be internal damage to a battery like electrolyte will boil and evaporate, but it will read 20V after disconnecting! And will slowly drop over time, if left unconnected.

And this happens quite frequently. Well, not 20V, but when one cell shorts out, car still charges battery with same 14-15V, so other cells overcharge. But if short does not increase internal resistance too much, you even won't notice that for a couple of months until there happens too much damage and internal resistance goes significantly up (meaning capacity drops to unusable level).

Now, if car COULD just overcharge battery, disconnect it and look at the drop, it could be possible to estimate something about it's state and capacity. But it's quite difficult to do in a car, given there always is something needing power. I doubt anyone would be happy to get to a car and see that it's currently determining battery state so can't be opened or operated for another 12h And all alarms are switched off because of that.

From all of this it SHOULD be clear, that car simply CAN'T distinguish degraded battery from a lower capacity one. If you put 80Ah of energy into it and it reaches 12.5V (or whatever volts, adjusted by temperature, chemistry, etc) you can't really know if the battery is 80Ah new or 105Ah degraded.

That is the reason you need to BOTH register battery change AND specify it's capacity. Then it's possible to tell that if you have put 20Ah of energy into quite discharged battery and voltage reached a certain number, but battery is supposed to accept at least 40Ah theoretically, then it's simple arithmetic to decide, that battery is quite degraded.

Well, even when using specialized battery tester devices used by mechanics, you STILL need to input its rated amps, capacity, standard or something similar.

But again, there ARE ways to figure that out by measuring additional parameters like acid density, etc, but car CAN'T do that. And most of new batteries are of a sealed type anyway, so you can't even measure that without destroying battery. There could be other more expensive ways to figure that out undestructively, but I would guess that they are all quite expensive to integrate into each car.

P.S. When I was young, I remember my father (and other motorists) used acid density measuring tools to prolong battery life. To decide whether add distilled water or acid. Car batteries were quite difficult to buy in USSR due to shortage.

[Raimo5]

Very well explained. Just to add that, if possible, you would want to use at least same capacity battery that the car was designed to. You can get away with using smaller capacity if you won't downgrade too much. I would strongly advise against replacing AGM battery with EFB or flooded cell.

In any case, replacement battery needs to be registered even if it's the same capacity. APM (I think BPM as well) keeps track of battery wear and takes it into consideration when determining upper and lower startability limits and general power management across platform.

[Tracshan]

Thanks to Node and Raimo5,

As it relates to 12.5v that figure was just an example, I am aware that this isn't a set figure. I have tested all sort of batteries and seen all sort of reading over the years.

[TitanicSnake]

Hi everyone, very interesting thread and responses.

May I ask a question on this matter?
Do you know why on a battery charged to 100% using a ctek mx 5.0 ISTA still shows less than 70% of SoC?
Battery is charged using terminals under the hood and not directly on the battery.
Is it because the ctek is determing that by only voltage?
Car is a F40 with EFB battery and battery health (according to ISTA) of 96%

This is a problem for example with OTA updates which require at least 70% 75% of battery charge.

Thank you

[Node]

It's really hard to tell. Little useful information was provided.

We have two things at play here. The actual state of battery and how the car perceives that.

Regarding a perception of a battery by a car: how OLD is the battery? It is PROPERLY registered to a car (I mean does the car knows it's EFB, or it thinks its AGM, same question about capacity)??? Is it QUALITY battery or some cheap junk?

Regarding actual state of battery. EFB batteries also need a different charging curve than usual flooded batteries. But they also are damaged by AGM charging curve. That charger does not seem to have a mode for EFBs. That COULD be a factor too as it will UNDERcharge EFB in a normal flooded battery mode.

Also, this CTEK has an internal temperature sensor. When charging under the hood, was the engine HOT? If so, it will decrease charging voltage, but the battery is a bit shielded from the engine in the F40, so it's temperature could have been significantly different.