ssalb

I don't think that 2005's originally came with AGM (Advanced Gas Mat) batteries. I think the switch was made sometime during the 2008 production run. My early 2008, which had it's original BMW battery (white case non AGM). You can switch them and put in an AGM battery, but you better have it registered if so.

If someone knows otherwise please correct me.

BimmerFan52

+1 Agreed.

The car does charge the two type of batteries differently, based on age, the type of battery, the condition of the battery (referred to as the battery State of Health or SoH) and the present State of Charge (SoC).

The SoC and SoH of the battery are read and stored by the Intelligent Battery Sensor (IBS), and if the electrical system is discharging the battery faster than it is being charged and the ambient temperature is low, the Digital Motor Electronics will signal the alternator to increase the voltage output and/or increase the engine idle if the vehicle is stationary.

The range of voltage output for the alternator can be 14.0-15.5V. However, the AGM type battery is only able to accept a maximum of 14.8V before damage may occur. Thus it is important that if an FLA battery is presently registered in the computer and an AGM battery is installed later the AGM battery type should be registered to prevent potential damage to the battery through over voltage.

If the correct battery type (FLA or AGM) and amperage ratings are registered in the computer then the other item to be registered is the age of the battery, calculated on each start up by subtracting the registered date of installation from today's date.

The DME uses an algorithm based on the calculated battery age as one of the factors, along with the SoC, SoH and ambient temperature in modifying the level and time of voltage output by the alternator.

As a battery ages its ability to accept a charge deteriorates and thus the voltage for an older battery will be applied longer, everything else being equal. This has the effect of electrical system potentially over-charging a new battery because the calculated date shows an older battery.

However, in practice many people have simply replaced their battery with the same type and amperage rating, skipped the registration of the installation date and experienced multiple years of good service. If you register the battery ($150 after market battery and $50 Indie registration) and get four years service or skip registration and get three years of service, the cost per year is equal.

Rizbel

This is the best explanation why there is a need to register new battery on late model BMW. I registered mine using coding (INPA/NCSExpert) when I switched to an AGM type battery.

Mason8DF

This would be a good start before you just go out and start replacing parts as they are not cheap!