I've had a 2018 Leaf SV for a couple months. For the first 2000 miles or so that I had it, I seldom used more than ~70 miles range before recharging, but I did notice on two occasions after longer drives that I got home with a lot less capacity remaining than I expected.
A couple weeks ago I forgot to charge at night, and during my commute to work the range started dropping precipitously when it passed 60% (or so), to the point that I wasn't sure I'd make it into work. Fortunately the rapid decline leveled off, and I got to work where I could charge.
After recharging, I spent that evening trying to reproduce the problem. Which turned out to be easy. I video'd this, and uploaded a portion of the video (below). There was a rapid decline to this point, but the real fun starts about 0:30 in. Note the ideal driving conditions (mid 70s, flat road, motor stays in the "eco" zone). The battery percent jumps all over but rapidly trends downward. Over the 8 minute video it starts at 39% and ends at 23%. I took a screenshot of Leafspy which appears to be showing one cell that has a lower voltage than the rest https://imgur.com/a/cCLHNm5
I took the car to the dealer for repair, and they returned it saying they couldn't fix anything because there are no codes being thrown. On the drive to work the next day I recorded a video (below), showing more or less the same behavior, but dropping from 48% to 25% over 8 minutes. I took the car to the dealer again, and again they said nothing was wrong, and that I shouldn't bring the car back to them.
While I've not tried to drive the car until I get stranded, by my best estimates my 150 mile Leaf will get perhaps 100 miles range on a full charge.
Does anyone have suggestions for next steps? Is there any way to "prove" to the dealer that there is a problem? The other Nissan dealer in town is quite a jaunt away, but I may have to visit them next. I've started pondering a lemon-law claim but that seems like a huge hassle, and I really just want my car fixed...
Thanks for any suggestions!