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Jump it and see if it happens again tomorrow. If so, run a voltage test to see if anything is drawing extra current and to make sure the alternator is charging the battery. If neither of those, then probably new battery time. How old is the battery?
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CanBUS, so once voltage drops below the required range, nothing will work as the brake light is unlikely to be a circuit that gets power all the time the ignition is on (even when low batt), hazards probably will though
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Most popular faults for a battery drain are Tailgate glass window switch, Does it open on its own at times when starting the car?, or if it has a panoramic sunroof the rear drains can block water then fills up the boot shorting out electronic modules.
When you do fit a battery fit same size and type and register the change in the vehicle electronics, if you go for a different size or type it will require programming.
Edit to add terminal 30G relay will switch off non essential electronics based on current draw measured by the intelligent battery sensor (they can go faulty as well) things like radio audio, heated rear windows, air con non essential items will be switched off to preserve battery voltage to allow the car to start so they switch off before it drops below 11.5 volts,
4.7v is a hefty drain.
To check for a current drain use an ammeter in line with the negative lead of the battery, we usually open all the doors and roll the door catches and boot, fit an ammeter in parallel, then wait 30 mins for the system to go to sleep then disconnect the earth lead at the body so now everything is going through the ammeter, anything over 60ma is too much, you can disconnect fuses to isolate circuits, but remember if you put any back in straight away you risk waking the car up and another 30 minute wait :)
I also use an infrared laser thermometer to measure temperature of components anything too warm is a suspect :)Where are you based?
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Double_J
BrickMan
Fixedwheelnut
@Dramatic_Hammer
BMW people, my E61 isn't doing anything electrically this morning... Won't unlock, lights don't work, radio doesn't turn on, won't turn over (obviously). I've got in via manual key and tested the battery (showing 4.6v) - this is clearly someway off 12v but I'm surprised brake lights at least don't work.
Anyway, new battery time or jumpstart/charge and see what happens? Either way I'm late for work and spending on parts & tools...