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Old 01-13-2013, 04:20 PM
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fun2drive fun2drive is offline
BMWCCA 149159
Location: Panhandle of Florida
 
Join Date: Nov 2005
Posts: 2,613
Mein Auto: 335 vert//M3/4/ 13Outback
Look the Intelligent Battery System takes a lot of variables into account for calculating how to charge the battery. It is not full proof and do you really think an AH difference if it is minor really matters? I think not given individual batteries have variance as well.
Also the registering the battery to let the IBS know you have replaced it is easily done with a labtop and a K+DCAN cable you can acquire on eBay or Amazon for not much cost.
http://www.e90post.com/forums/showthread.php?t=727091
The site above will take you to a member of another forum that has a download allowing you to register your battery for free. I have downloaded this software and tested it out on my 335 and it works just fine registering it.
I am not affilated with that members work at all but there are things you can do yourself.

Coding is also required if you are way off the AH rating of the battery you buy. However if you are close, good enough really.
There are You Tube videos out there that show you how to disconnect the IBS cable so you can remove the assembly without blowing a fuse.

Yes you can screw this up but if you are careful you should have no issues replacing the battery.
BMW uses two batteries vendors (Excide manufactured by Bosch by the way and Douglas). Find an Excide-Bosch/ Douglas battery that fits the AH and dimensions your BMW needs (stamped on the battery) and you should be good to go.

I do admit this is an unnecessary complxity because no one knows except BMW how much this improves battery life.

Locking your car is about the best way to help your battery since the ECU will turn on every 4 hours and ping your system, locked it doesn't turn on...
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