Battery disconnect

paulcurtis · 03-23-2009, 09:44 AM

Hi all,

I've not found a definitive answer for this yet, so im hoping someone can help.

If i disconnect the battery (key out) then what will I loose when the battery is reconnected?

Do systems need to be initialised?

The car radio unlocked? (I have no idea what the code is, the car is 2nd hand)

just wondering before i do it!

cheers
paul

FotiosF90M5 · 03-23-2009, 10:44 AM

the ONLY thing you lose it the time and date. i think mpg and that sort of thing too.

F104 · 03-23-2009, 12:39 PM

Quote:

Originally Posted by fotios335i

the ONLY thing you lose it the time and date. i think mpg and that sort of thing too.

indeed that's all you loose. Do not disconnect the battery while the light in the starter button is still on, the ECU will be pulling 4 Amps while the light is on (about one minute). Then current draw drops (forgot to how much) and after 30 minutes from closing the door it drops to 40 milli-amp or less. So best is to take out trunk light, leave trunk open, close door, wait 30 minutes, and then disconnect it

FotiosF90M5 · 03-23-2009, 12:48 PM

I just disconnect it...lol

SoCalTech · 03-23-2009, 04:06 PM

Active steering will need to be initialized.

SoYank · 03-23-2009, 04:46 PM

Quote:

Originally Posted by F104

indeed that's all you loose. Do not disconnect the battery while the light in the starter button is still on, the ECU will be pulling 4 Amps while the light is on (about one minute). Then current draw drops (forgot to how much) and after 30 minutes from closing the door it drops to 40 milli-amp or less. So best is to take out trunk light, leave trunk open, close door, wait 30 minutes, and then disconnect it

Aha! So THAT's how the dealership can get away with charging an hour's labour for a thirty minute job.

FotiosF90M5 · 03-23-2009, 04:50 PM

Quote:

Originally Posted by F104

indeed that's all you loose. Do not disconnect the battery while the light in the starter button is still on, the ECU will be pulling 4 Amps while the light is on (about one minute). Then current draw drops (forgot to how much) and after 30 minutes from closing the door it drops to 40 milli-amp or less. So best is to take out trunk light, leave trunk open, close door, wait 30 minutes, and then disconnect it

whats the reason for doing this. im curious. thanks

greatbm · 03-24-2009, 02:08 PM

Quote:

Originally Posted by fotios335i

whats the reason for doing this. im curious. thanks

A charging battery gives off explosive gases, whilst under load the disconnection will draw an arc and could ignite causing explosion. As the battery is in the boot BMW vent the battery via a small pipe to under the car. It is just good practise to dissconect this way.

CdnE90 · 05-15-2009, 04:21 PM

Quote:

Originally Posted by SoCalTech

Active steering will need to be initialized.

How does one go about doing this? Can I do it, or do I need to take it to the dealer?

SoCalTech · 05-15-2009, 08:42 PM

Dealer only.

03-23-2009, 09:44 AM	#1
paulcurtis Private 11 Rep 52 Posts Drives: 120d/320d Msport e91 Join Date: Jan 2009 Location: Kent iTrader: (0)	Battery disconnect Hi all, I've not found a definitive answer for this yet, so im hoping someone can help. If i disconnect the battery (key out) then what will I loose when the battery is reconnected? Do systems need to be initialised? The car radio unlocked? (I have no idea what the code is, the car is 2nd hand) just wondering before i do it! cheers paul
	Appreciate 0 Tweet Quote

03-23-2009, 10:44 AM	#2
FotiosF90M5 ///M Specialist South Shore BMW 801 Rep 7,109 Posts Drives: 2021 M5 Comp BHG/Silverstone Join Date: Jan 2007 Location: South Shore, MA iTrader: (62)	the ONLY thing you lose it the time and date. i think mpg and that sort of thing too. __________________ 2021 M5 COMPETITION LCI Brands Hatch Gray on SIlverstone, carbon roof, comp wheels, Mperf splitter, carbon pro spoiler, carbon diffuser , carbon paddles, executive pkg. Dinan HAS, RaceChip, dinan spacers, FC stud kit, etc
	Appreciate 0 Quote

03-23-2009, 12:48 PM	#4
FotiosF90M5 ///M Specialist South Shore BMW 801 Rep 7,109 Posts Drives: 2021 M5 Comp BHG/Silverstone Join Date: Jan 2007 Location: South Shore, MA iTrader: (62)	I just disconnect it...lol __________________ 2021 M5 COMPETITION LCI Brands Hatch Gray on SIlverstone, carbon roof, comp wheels, Mperf splitter, carbon pro spoiler, carbon diffuser , carbon paddles, executive pkg. Dinan HAS, RaceChip, dinan spacers, FC stud kit, etc
	Appreciate 0 Quote

03-23-2009, 04:06 PM	#5
SoCalTech Captain 24 Rep 648 Posts Drives: Not a BMW yet... Join Date: Oct 2008 Location: Redondo Beach, Ca iTrader: (0)	Active steering will need to be initialized.
	Appreciate 0 Quote

05-15-2009, 08:42 PM	#10
SoCalTech Captain 24 Rep 648 Posts Drives: Not a BMW yet... Join Date: Oct 2008 Location: Redondo Beach, Ca iTrader: (0)	Dealer only.
	Appreciate 0 Quote