[JimD]

That is good data, mleskovar. That voltage information is also what the car looks at when deciding how/when to charge. When my car died on the side of the road due to the alternator, the AAA guy looked at the voltage and told me he didn't think it was the battery.

Since my last post on this thread I've learned of another related reason that BMWs are "special" with respect to battery charging. Our cars do not routinely fully charge our batteries!! BMW is seriously into saving the planet and uses the alternator to charge the battery as we deaccelerate. Sending the alternator the demand for the current to the battery increases the engine power to the alternator slowing the car a tiny amount. It is using kinetic energy to replace friction in the brakes. That kinetic energy is then stored in the battery for future use. But if the battery was fully charged, it would not be able to accept this additional charging when we slow down. Hopefully this makes some sense.

So due to this minor hybridization of our cars, it is more important for the car to know what sort of battery, and how old a battery, it is charging. Thinking it is an old one (like mine, still original) could more easily result in over charging since the car would do more normally and think it is still able to do the brake thing.

The only risk of not coding that I consider credible is over charging the battery. Replacing a battery every 5 years instead of every 10 years or so wouldn't justify in dollars what the dealer charges. But I still think it justifies a few minutes of my time.