Infuriating situation that happened before with my E53 and now it's happening with my E70.



I have a battery that lost most off its storage capacity but when fully charged it will push 700 CCA. (So it passes the cranking amps test and so they won't replace under the warranty).



The problem is compounded by a couple things:



1) the car only charges the battery to 80% so that it has a cushion or overhead to charge when coasting to save energy=gas.



2) the car pretends to go to sleep in 15 minutes but the accessory relay (30g terminal relay) stays on for 30-60 minutes.



Well my battery capacity has degraded enough that when charged to 75-80 it may drop to 60-65 during that 30 minute window where the car is pulling 2.5a from the battery leading to a low voltage no start condition in the morning.



"All signs" point to a parasitic drain and when i first started to diagnose I noticed the 30g relay was quite warm (using IR camera), but it just warms up quickly and kicks on the moment you unlock the car with the remote or open a door if not locked.



In an effort to keep my car working until hopefully i get my case escalated to where they will replace the battery or I bite the bullet and replace it out of warranty, i did a couple things to mitigate my non start after sitting overnight.



1) i coded the cas to shut off the terminal 30g using Bimmercode in expert mode after ten minutes vs. 30.



2) i coded the trunk to not turn on 30g from tailgate operation but that disables the trunk motor so i have to unlock the car first if i want to use the auto trunk lift. An acceptable trade off for the week or so i anticipate dealing with the problem.



3) i unplugged the IBS cable from the battery negative terminal. This has the effect of running the alternator full time and will top off the battery so i have 85-90% state of charge in the morning vs 60-75% and random chance of needing to use my jump starter.



So, the main point of sharing is to bring up a common type of battery failure that gets missed because it will "test good". I spent over a week trying to find a non existent parasitic drain largely because the car pulls 9a when first locked, 2.5a for about half an hour which i only recently discovered and thought (silly me) that when it "went to sleep" at 15-16 min. (evidenced by the start button going dark), it should stop pulling power. Well it might "sleep" at 15 but it doesn't "deep sleep" until 30.



My battery is sulfated to the point i got low battery based errors from listening to the radio for under ten minutes so that's probably more than 95% loss of amp-hours. Something unfortunately the battery sellers never test for. It'll have to get down to like 98% loss so it won't pass the CCA test.



The test i used to use was hazards but with LED that's not a great test. My new test for loss of capacity is to monitor voltage while listening to the radio (bonus less boring than just watching hazards flash). I got a 4x4 error on the iDrive when voltage dropped. I wasn't watching how low that got but iDrive stored an under voltage error.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)