Battery Life Remaining on 2015 i3 w/37k at 17.4 kWh

Using the hack to check battery life, I found my battery at full charge listed at a capacity of 17.4 kWh. I viewed a video made 2 years ago (thus when the car was 3 years old) for a 2015 i3 with 12k miles which showed 19.4 kWh.

My capacity was read at 46 degrees F. Is the capacity presented affected by outside temperature?

Is 17.4 kWh capacity considered to be normal degradation after 5 years of moderate use? I'm quite sure that this was a commuter car that also charged at work, thus possibly lots of 100% charges.

Any other thoughts on this subject will be appreciated.

Our 2014 BEV has been driven only 11k miles, is almost always charged at only 16 A @ 208 V (< 5 DC fast charges), is normally not charged to full, has almost never been left full for many hours or days, and has never experienced cold or very hot temperatures (Honolulu); i.e., it has led a pretty ideal EV life. Yet Batt. Kapa. max is only 15.2 kWh, down from 20.9 kWh in November, 2016. This agrees well with its actual range and efficiency readings (reset trip meter, drive a long distance, divide the distance driven (mi) by the efficiency for this trip (mi/kWh) to get the kWh consumed, extrapolate the percent capacity consumed to 100% to get the usable capacity).

The degradation rate of Li-ion battery cells increases with an increase in the number of charge-discharge cycles, in their age, in the amount of time the cell remains at a very high or very low charge level, in the average depth of discharge, in their average temperature, and in the average charge level. None of these explains why our battery pack has degraded as rapidly as it has. Or maybe the fact that I've stored our i3 for a total of 2 years ranging from 3 to 9 months each storage period has somehow increased the cell degradation rate even though the charge level was ~50% and the ambient temperature averaged < 80 ºF during storage. Or maybe the battery management system has been gradually reducing the usable capacity to decrease the cell degradation rate to minimize BMW's risk of battery pack capacity warranty claims. Who knows?

Fortunately, only some 60 Ah i3 owners are reporting significant actual range loss. 94 Ah and 120 Ah i3 owners don't seem to be suffering significant range loss, at least yet. So newer battery packs don't seem to be degrading very fast.

Randy101 said:

Is 17.4 kWh capacity considered to be normal degradation after 5 years of moderate use?

Click to expand...

It seems likely that this is in the realm of "normal". BMW or Samsung are probably the only ones who could answer for sure though. It actually sounds pretty good compared to what I've seen by tracking my car (thread here: https://www.mybmwi3.com/forum/viewtopic.php?f=11&t=17163). From that info and and what others have said, it seems like degradation might be around .00015 to .00020 kWh per mile driven (with a starting point around 20kWh new). The degradation does not appear to be exactly linear though so that straight line fit is just a rough approximation. Using that formula would suggest your car would be somewhere around 14.5kWh so by that comparison you're in pretty good shape. Ultimately though, all that really matters is if you have enough range for your needs. Hopefully you do!

Also, FWIW, mileage also seems like a better factor to determine battery degradation than age because of the direct correlation between mileage and charge/discharge cycles.