Quote:
Originally Posted by gbalthrop
I would be interested to know WHAT INPA screen you are referring to. For instance, DME > F5 > F5 > F2 PM (Power Management) Infofield 2, provides values for "Ladungszustand & Startfähigkeit" = State of charge & Starting ability, at the moment (last start), and for 1 day ago to 5 days ago (vor 1 Tag to vor 5 Tagen).
There is a LOT of data in INPA, and the problem I have is trying to correctly interpret it. As a practical matter, I have NEVER seen a battery fail to crank the starter of ANY vehicle for 2 seconds, at ANY temp > 10F, as long as its voltage measured 12.0 Volts or more. In warm weather, most will crank if > 11.9V.
George
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Bimmerprofs has some posts about the IBS discussing the INPA IBS pages, but I'm not sure their conclusions are correct about all of it.
https://bimmerprofs.com/ibs-non-registered-battery/
https://bimmerprofs.com/replacing-the-battery/
https://bimmerprofs.com/battery-dont...stered-really/
I've watched the SOH reading go to 0 immediately after registering a battery. It increases from there (over months and years) and readers show it as 100-(read value) = "Remaining Health" so my 11.72 is 88.28% health left.
From what I've read, the SOC reading isn't accurate most of the time. I think I'd read that when the car is powered fully off (as in all modules in sleep) for 2 hours, then it takes the battery voltage and temperature and computes an accurate state of charge at the moment. I think that's still available to be read if you read it before starting the car, but after that, it seems like it wanders around way too quickly. I'm curious what the start capacity readings are. In theory, with a fairly good reading of Ah in/out from one high accuracy SOC reading to the next, they should be able to calculate the total remaining capacity of the battery.
The remaining capacity will drop slowly over the life of the battery and it doesn't always mean much as far as being able to start the car, but as that total Ah capacity drops below ~50% of new, lead acids tend to become unreliable and that's when you might suddenly have a loss in cranking ability. I had a 7 year old battery that had been fully drained by failed alternator and after I got the alternator sorted, I measured it's capacity with a full charge and discharge - 27Ah. It worked just fine with the alternator, but at that age with that much capacity loss (Rated at 90Ah, I think) I felt OK about
replacing it at my convenience.