Just replaced my battery for our '07 328i yesterday. Simple and straight forward for the average DIY'er. I did not see this tutorial until after-the-fact.
The car began cranking slow while I was out of town. I had my daughter put a trickle charger on it overnight. The next morning, it was still showing a 2 amp draw. I assumed we had a bad cell in the original battery (~ 61,000 miles). The dealer wanted $299 ($201 for the battery itself) for a new battery and install. I looked online and ALL sites (Interstate, Pep Boys, Autozone, Advanced) called for a group 95R battery. My service advisor said to just go buy a quality battery and put it in, no mention of registering the battery (I'll call tommorow, get the skinny and report back)
I had my wife pick up an Interstate MTP-95R/H9 that I was able to get for $179.95 plus tax. (I would have gone with the dealer battery as I could have got a 10% discount and paid the same but the dealer is a 40 mile round trip and that cancels any savings). I took the old battery out and set it by the new one. SURPRISE! The new one was about 2 inches longer, there was no way it would fit and the Interstate dealer was closed on weekends. I needed a battery right away and could not wait until Monday.
I started to search and found that a Group 94R/H8 battery was the same size as the original. I went to the local Autozone and found that they had two batteries in this size. One was a standard lead acid Duralast Gold with an 85 month warranty and the other was a Duralast Platinum (Not listed on their website) with a TON of cranking Amps. The Platinum battery is an AGM (Advanced/Absorbtion/absorbed Glass Mat) battery in the H8 group. The drawback here is that the warranty is 3 years PERIOD, no proration after that and it was the same cost of the standard lead acid battery. I got the manager to give it to me for $119 because of that fact. The battery however, will never leak, spill or need venting (although I still installed the vent tube).
I installed the battery and the car works fine with no warnings. I did have to reset the clock and date, radio stations remained stored. The problem with AGM batteries is that they are very sensitive to overcharging and will be ruined if they are. If it is true that the BMW system starts putting extra charge into weak batteries and subsequently needs to be "reset" after an new one is installed, I'll have to do this right away so I don't fry the AGM battery.
I'll report back after I talk to the service writer and an independent shop locally that I trust.