I was surprised to note that I lost my first capacity bar today @ 15,600 miles on my 2011 SLE.
I would contend that my car has been the most "babied" Leaf out there, to wit:
I've Never QC'd; I've never seen more than 6 battery temp bars; My car has never been located where the temperature exceeded 90 degrees (I live 6 miles from the beach in San Diego); I've never driven it to turtle, or even VLBW; I've charged to 100% less than a dozen times since new. About 90% of the time, my battery SOC is between 4-7 bars when not driven for several days. I've done 95%+ of my charging at night in my garage with my level 2 EVSE, using the car timer. My car is almost always in a cool (65-75 degrees) garage when not being driven. I drive in ECO 100% of the time.
I'm technologically challenged, so I don't have any devices to measure battery capacity like a lot of you folks do. But, I'm surprised to have lost a bar with such low mileage.
Since my car is now 2 1/2 yrs old, I guess that time is just as detrimental (or more so?) than temperature, regarding battery degradation. I still intend to drive this car for at least another 5 yrs on my original battery. Of course, not having to commute (did that for 35+yrs) gives me lots of options.