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      03-20-2011, 07:09 PM   #1
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Drives: 2011 M3 Coupe
Join Date: Jan 2011
Location: San Jose, CA

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Battery Disconnect Q?

Perhaps a stupid question, but thought I should error on the side of caution. Rather be safe than sorry and all that.

When you disconnect the battery, does the car "forget" any of its settings? Or is it just a non-event? Does the length of time it is disconnected have any varying affect? And it's the negative side that should be disconnected, right?

Thanks for the help.
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      03-20-2011, 07:37 PM   #2

Drives: 2008 E92 M3
Join Date: May 2010
Location: SoCal (Irvine & LA)

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I had my battery disconnected for ~5 hours yesterday while installing the BMW performance wheel. After putting it back in, the only thing that was reset appeared to be the clock. All my radio stations and bass/treble were still set the same.

Note I do not have iDrive, navi, etc. I have the basic M3 with only EDC. I'm not sure what crazy stuff the iDrive has since I never used it before.
2008 E92 M3 | 2007 Honda S2000 | 2001 Honda S2000 | 1997 Turbo Integra
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      03-20-2011, 09:59 PM   #3
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Drives: E90 M3 6MT
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When disconnecting the battery I always disconnect the ground and tape it so that it doesn't have the chance to fall and re ground itself to the car messing up my computer and all that. Second the only thing that should reset is the date and time. No other settings should be reset such as seats, edc, radio stations, etc.

E90 ///M3 6MT Atlantis Blue - Fox red #TEAMMODE
ESS VT1-550|Volk TE37|Recaro|STOPTECH|Ohlins R/T|Mode Carbon GT4 Lip|Umnitza V4 |Agency Power/Sosi/ACM Test Pipes|BMW PSW V1|
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      03-20-2011, 10:08 PM   #4
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Usually everything resets when disconnecting battery, so if it doesn't on this car, it'd be the exception. Based on Shamoo's input, the M3 is an exception to that rule . Good to know.

As a related comment, if you swap a charged battery for a new one with the same ratings (also charged), the car shouldn't need any 'coding' then, right? Or disconnecting the '+' as well erases everything? Curious.
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