Battery discharging whilst parked

[JamesInLondon]

Hello All
I have a 2016 94Rex with 20,500 miles, last week I received the dreaded "Battery Discharge whilst stationary" message, checked on here & immediately booked it into my BMW agent for replacement of the 12v battery. This is scheduled for next week.
On Thursday I parked the car with 99% battery level after charging it at home, this morning when I went to it, the battery level was only 51.5%.
Are these two phenomena linked, or are both of my batteries on the way out?
I hope not, because I love the damned thing, always makes me smile whenever I get behind the wheel.

Thanks all

 

[EvanstonI3]

So that is a week you left it?
If the 12v battery is failing to hold a charge, the main battery will come on to try and boost the 12v to "keep it alive".
If the 12v is not holding a charge, all that energy just gets turned into heat and the main battery will always be on, trying to charge the 12v.

I suspect that is why you got that message and also why the main battery drained that much over a week.

 

[JamesInLondon]

Thanks for the speedy response

 

[JamesInLondon]

So, 15 months and 3.5k miles after the new 12v battery, the dreaded "Battery Discharging whilst stationary" message has returned.

The message disappears as soon as I engage D, the main battery seems to be maintaining its charge pretty well, could the 12v be failing after such a short time?

The car sits for between 3 days and a week in between being driven, could this have any effect on the 12v battery?

Thanks in advance for any advice.

 

[alohart]

The car sits for between 3 days and a week in between being driven, could this have any effect on the 12v battery?

Yes, I experienced the same thing during the pandemic when our i3 wasn't driven much. Apparently, the vampire always-on 12V loads were slowly discharging the 12V battery until the warning was displayed. I fully charged the 12V battery with a battery charger which got rid of the warning message for probably 6 more months of little driving when it appeared again. The 12V battery was just discharged too much, not failing.

That said, your battery could be failing prematurely. However, if you have a 12V battery charger, try fully charging the battery while also identifying where you could buy a replacement should you need to do so. I ended up buying a replacement and storing it until the installed battery really was failing. I charged the stored battery every 6 months or so to keep it from self-discharging too much.

 

[Dutchi3]

The car sits for between 3 days and a week in between being driven, could this have any effect on the 12v battery?

With a good 12v battery, a week of no driving should not be a problem, I can tell from experience and probably others too. That would be ridiculous. I never got that message, until my 12v battery was really dead in the end. Maybe as alohart said, the 12v battery may be failing prematurely, a rare case but possible.

 

[EvanstonI3]

could still be a failing 12v battery.
While "most" seem to last 3-4 years, there are some outliers reported that have lasted TEN YEARS and some that have failed within a year. Not many, but statistically still possible.

 

[mojo]

It could be another failing battery, but I have seen the same message in my car after leaving it for 10 days while on holiday. The HV battery was ~60% at the time and may have dropped 1% during the 10 days. My car is only just over 3 years old. So I'm hoping that it's not unusual to see this if the car is left for a while...