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      10-30-2010, 06:53 PM   #81
Brigadier General

Drives: 4runner SR5
Join Date: Mar 2007
Location: MD

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2007 BMW 335  [4.50]
Originally Posted by 401FlaGATOR View Post
I'd like to chime in on why you probably need to register AGM...

AGM (absorbed glass mat) have an advantage compared to SLA (sealed lead acid) in that they lose less electrolyte in hot dry climates and they vent very little gas. However the technology has a disadvantage to SLA in that they have a higher internal source resistance and therefore less CCA (cold cranking amps) than SLA. Therefore you get larger voltage drops than you would with SLA. Methinks this is the reason for the registration process. To "register" the voltage drops somehow? I may be wrong just my educated guess...
Nope. It's a little more complicated than that. Everything is answered in an $85 Bentley Manual off of Amazon. Anyone keeping the car more than a couple years should invest in that manual and a bavarian techniq scan tool for about $289 (especially for the 335 with so many issues with coils, injectors, etc). Not to mention, they will be adding the ability to register the direct injectors soon. You can do everything at home and recoupe your costs for those two expenses many times over.

I would have to go look at the manual again, but there are quite a few computers on the car's network, and probably somewhere around 3-4 dozen sensors.

I tried out a lightweight battery and went back to the OEM. The light weight just was not high enough capacity for my 1-2 days a week of driving the car.

Battery registration is a good idea, and there are enough people with the bavtec tool that someone in the regional forums may be willing to let you use theirs for no cost. Literally takes a couple of seconds to send the command. I agree the dealer is a ripoff for that service.