[JimD]

I found the attached interesting. Apparently the logic for charging the battery is fairly sophisitcated in our bimmers and it needs to know when you put in a new battery so it charges it appropriately. It matters if it is AGM - some sort of mat instead of just water/acid - or conventional water/acid (which is basically not recommended since it gives off more gas and the battery is inside the car). It also matters if it is old or new and I'm sure the size matters too. The article describes the process.

"Registering" is basically telling the charging logic that the battery is new and a little information on the battery. The penalty for not "registering" is potentially shortened battery life. You need a better OBD-II interface than I have but people other than a dealer should have it.

Jim