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post #1 of 16 Old 18th March 2019, 03:56 AM Thread Starter
flacoramos
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battery discharge info

Have been doing a bit of troubleshooting on the increased battery discharge messages I've been getting and thought I'd share what I found. The IBS monitors for increased battery drain (>80mA) while vehicle is off and the results can be read with ISTA. So no need to measure current as few other members have been doing lately. See screenshot showing good results for 'only' the last 32 cycles.
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post #2 of 16 Old 18th March 2019, 03:56 AM Thread Starter
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Another interesting bit is that the DME/IBS calculates a 'startability' threshold based on temperature, battery state of health (this one I haven't figured out how to read...), among other factors, see picture. If the battery level falls below the calculated threshold it will trigger the error, even if there's nothing draining the battery.
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post #3 of 16 Old 18th March 2019, 03:56 AM Thread Starter
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Now... remember that after the car is parked / shutdown / locked the car itself will wake up after a few minutes and do god-knows-what... ISTA shows a graph of current vs. time showing this being the expected behavior. I believe it's during this housekeeping cycle that the battery charge can fall below the startability threshold (voltage threshold really...), thus the IBS/DME will shutoff power to the radio/cluster/etc. and trigger the increased discharge message on the next cycle.

In my case I've gotten the increased discharge messages only during winters. Which makes sense but car has never failed to start. My battery is about 5 yrs old and testing always showed CCA being ok but not good enough for the IBS it seems (what battery testers think an OK CCA drop is isn't clear...). So I ended up replacing the battery. Will likely have to wait until next year as temps have started to go up around here.

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post #4 of 16 Old 18th March 2019, 03:14 PM
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This is a lot of good information, thank you for breaking it all down.


I also have gotten the battery discharge warning in the IDRIVE but have never had issues starting the car. Figured it was a combination of a battery on its way out and the M5 not getting long enough frequent trips for the alternator to do its job well enough. I've taken it out every 4 days or so until it at least gets to operating temp and I haven't had the message come back.


It seems to me these cars really like to be driven. If they sit for too long things start getting wonky.
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post #5 of 16 Old 21st March 2019, 10:20 PM
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So, bad programming by BMW?

Quote:
Originally Posted by flacoramos View Post
Now... remember that after the car is parked / shutdown / locked the car itself will wake up after a few minutes and do god-knows-what... ISTA shows a graph of current vs. time showing this being the expected behavior. I believe it's during this housekeeping cycle that the battery charge can fall below the startability threshold (voltage threshold really...), thus the IBS/DME will shutoff power to the radio/cluster/etc. and trigger the increased discharge message on the next cycle.

In my case I've gotten the increased discharge messages only during winters. Which makes sense but car has never failed to start. My battery is about 5 yrs old and testing always showed CCA being ok but not good enough for the IBS it seems (what battery testers think an OK CCA drop is isn't clear...). So I ended up replacing the battery. Will likely have to wait until next year as temps have started to go up around here.
Basically the IBS does not account for the normal wake up behaviour of the car?
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post #6 of 16 Old 22nd March 2019, 02:44 AM Thread Starter
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Quote:
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Basically the IBS does not account for the normal wake up behaviour of the car?
I'm not following your logic there... If the battery voltage drops below whatever the startability threshold during the housekeeping cycle then it will give you the warning on the next cycle. The most likely cause for a larger than expected voltage drop would be a weak or discharged battery. Also if you've extra electrical equipment on the car then the housekeeping cycle could also turn those loads on and cause a large battery drop. Just guesses here tho.

IMO sure it's a bit conservative with cold temperatures. BUT at the same time it's done it's job right? I've never needed to jump-start the car so...
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post #7 of 16 Old 27th March 2019, 07:52 PM
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I am saying it may be oversensitive

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Originally Posted by flacoramos View Post
I'm not following your logic there... If the battery voltage drops below whatever the startability threshold during the housekeeping cycle then it will give you the warning on the next cycle. The most likely cause for a larger than expected voltage drop would be a weak or discharged battery. Also if you've extra electrical equipment on the car then the housekeeping cycle could also turn those loads on and cause a large battery drop. Just guesses here tho.

IMO sure it's a bit conservative with cold temperatures. BUT at the same time it's done it's job right? I've never needed to jump-start the car so...
On a side note, since it has the capability of commanding certain components to shut down, why doesn't it do that (one at a time) and see which one is misbehaving?
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post #8 of 16 Old 28th March 2019, 05:46 AM
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post #9 of 16 Old 28th March 2019, 07:00 AM Thread Starter
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Quote:
Originally Posted by 335xi View Post
On a side note, since it has the capability of commanding certain components to shut down, why doesn't it do that (one at a time) and see which one is misbehaving?
I don't think that's a true statement. I'd have to look at wiring diagrams, but pretty sure it's all or nothing.
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post #10 of 16 Old 28th March 2019, 07:42 AM
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