I own a 2014 BEV and had been keeping a log of the battery kappa max after noticing marked range decrease. Before I started logging I brought the car to the dealership with the concern and was told there was nothing wrong, not having any idea what tests are even performed for that result. The GOM would decrease fairly rapidly even while standing still once the battery reached around 40% yet the kappa max reading never went below 15.0kWh, which is above the 70% capacity mark where the warranty triggers. Skip 1.5 years to this spring and the car is getting only 50-55mi actual range (GOM would always indicate at least 65mi) on a full charge. Kappa is still 15.0kWh.
Not sure whether my battery warranty is 8 or 10 years (this is the 8th year) I took the gamble and had the dealership perform the battery warranty test. I had to specifically ask for a "battery test for warranty purposes" to get to that point. I was told that the test takes 2.5 hours worth of labor and should the batteries pass I would be on the hook for $600(!). I suppose this is BMW's way of dissuading owners from filing warranty claims. I nervously signed the estimate.
Two days later I received a call from the service rep to tell me that the batteries failed (whew!) and that the replacement batteries would be coming in from Germany and take approximately 3-4 weeks to arrive. The test returns only a pass or fail (what is this, grade school?). When I took back the car to await the arrival of the replacement battery it seemed that the techs had upgraded the Body Domain controller firmware to do the test because all the coding changes I had made to that module was reset and the battery icon next to the GOM had changed. Coding changes to the other modules were intact however. Also the GOM shows correctly that 55mi is the most I could travel on a full charge. This observation along with others account of seeing their range go up after requesting the same test seems to mean part of the test is making the BMS re-learn the battery.
Fast forward 3 weeks and the batteries had arrived. Took the car back to the shop and 4 days over the weekend I get my i3 back with a battery capacity like when it came off boat from Leipzig.
I gambled against a $600 labor charge that my 2014 BEV i3's HV battery is below 70% capacity despite the kappa max reads 15.0kWh and fortunately won.
Do not depend solely on the kappa max reading to measure your battery capacity.
Drive a significant distance without turning off the motor and record distance traveled, charge levels at start and end, and measured consumption rate of that drive using eDrive. Then use the formula "distance_traveled÷consumption_rate÷(charge@start-charge@end)÷nominal_capacity" to get you a better approximation to decide whether to ask for the warranty test or not.
For those interested, link below to the work order with service codes performed during the battery replacement.
EDIT: fixed typo iDrive→eDrive, clarified equation and added one more observed detail after taking car back before battery replacement.