I had my Leaf serviced at 24,500 kilometers approximately. The service includes a battery report and my cars battery (which is not the same as a laptop or phone battery) still has 100% capacity. Nissan have also recalled the original owners manuals which stated to only fast charge once per day maximum and as little possible. New manual says you can fast charge multiple times per day without adversely affecting lifespan of battery.
Each Nissan Leaf has a built-in internet connection (no rental/subscription required) and this is uploading data on the battery back to Nissan every week. They have a very good idea on how their batteries are doing and I believe this is the reason they have changed their advise on fast charging.
A Nissan Leaf in Japan has also managed to reach 250,000 kilometers on the original battery, this was done by averaging 6 fast charges per day. The battery has degraded, but is still running the car fine.
But that is pretty cool. The only thing is there are and will always be far more fast 3 phase a.c charging, so maybe the leaf II will have that, I can't see why they only upgrade 2014 Leaf to 6.5 kw and Zoe can charge @44 kw from 3 phase a.c ?