Yep, that's what I've heard too (about staying between 40% - 60%). I rarely charge it to 100% and if I do it's because I'm going on a slightly longer journey and I drive the vehicle within a short time after charging has finished.
On that note, I saw a YouTube video last week where a guy was using Leaf Spy on the used Leaf (2012 I think) he bought that used to be a taxi. Leaf Spy (and Soul Spy too I'm pretty sure) shows how many times your vehicle has been DC quick charged and this one showed that this former taxi had been quick charged about 7000 times! Battery capacity was in the low 70s, which is not great, but considering that kind of abuse, I have to say I was pretty impressed! Especially for the notorious Nissan Leaf battery.
Anyway, I will probably hook mine up on my next days off and see the SoH for my battery pack. I bought mine used but it had very low miles on it (only about 17000 miles on a 4 year old car. Not bad!), so I expect the battery SHOULD be in pretty good shape.
Kissimmee, Florida USA
"Even 93 miles of range is 3 times farther than the average person drives in a day."