The 6er puts a huge drain on the battery due to all the electronic sub-systems. When the battery starts to fail due to age it is common for the car to have multiple random errors due to the lack of voltage - things like rough engine, emission warnings, transmission errors, etc...
If your battery is about 5 years old then I would replace it. If it's less than 3 years old I would have it tested by your local PepBoys or AutoZone for free before replacing it. An OEM battery costs ~ $220 at the dealer. You can buy just the battery and have a BMW indie mechanic install it and have it registered for a lot less than what the dealer charges.
Registering the battery tells the computer that a new battery is installed which changes the way the battery is charged. As the battery ages the car will increase the voltage when charging.
Straight lines are for fast cars...turns are for fast drivers
'04 M3 - track
'06 650i Cab - daily driver
'02 Highlander - kid hauler
'01 330Ci - winter beater
Last edited by Yorgi; 01-03-2012 at 09:57 PM.