Originally Posted by swamp2
HP Auto claims that a "registration" of the battery is required for the entire system to take the smaller battery into account. Something that you can not do without the GT1 tool. I'm not entirely sure that the cars system is "aware" of the reserve capacity (it is certainly aware of the steady state output). I will let them perform this on the 27th at So Cal Euro and will update the results here. I'm not hopeful.
It would be great for you to make some suggestions about alternatives. We will all benefit from that and from your experiences. You are aware of the large physical size of the OEM E92 batter right?
Registration only takes into account a stored reading of battery capacity at 80%, odometer reading and refreshed stored temperature statistics. This will not aid in charging.
We're using the 21lb Braille in our M3 and 17lb in our 1-series project, the 1-series is a daily driver with no problems, the M3 needs to be started up about once a week.
Smaller batteries simply have less reserve capacity at a cost of shaving weight - drive often.