"Maybe he uses DC fast charging too much. Those chargers put a tremendous strain on the battery and regular use will quickly degrade its life. They're for occasional long-trip recharges."
Actually, that's not true. Fast charging every day may reduce the battery capacity by 1% per year at worst. There's an example of a LEAF used as a taxi which was fast charged multiple times a day and covered 130,000 miles before it lost the first battery bar. In fact, the observation seems to be that age is the killer so a car will lose capacity whether you use it or not, and in fact leaving the car charged to 100% or run flat (not that the car lets you do that) for long periods are what will damage the battery most. The early batteries also suffered in hot climates but the recent lizard batteries are much better. My own battery actually increased in capacity after a long hot run with three fast charges in a single day.
There's no reason to fear using the car regularly, or using fast charges. Also, replacement costs for the batteries are coming down considerably too and there's an opportunity for aftermarket upgrades with new technologies. The newer NMO battery cells which are planned for the next gen LEAF will allow a 60kWh battery to fit in the space of my 24kWh battery more than doubling range assuming someone is able to put them on the market for the older cars which would be a potentially large market anyway. Meanwhile, I'm enjoying my car, doing long trips and using the fast charger network happily without producing any emissions (my country is largely run on non-fossil produced power.)