The Industry experience so far:
The Nissan Leaf came out in 2011/2012. It is the most popular electric car in the world with over 250,000 sold.
Early Nissan Leafs are over 10 years old, and many are still showing great battery health. There are early Nissan Leafs operating in England with over 150,000 miles. A well-looked-after vehicle with 100,000 miles on it will normally have only lost 5 or 10% of its capacity. And this is all on the old battery technology. Every new generation of EV brings with it new and improved battery packs. We can safely say that EV batteries are not a disposable item, and will outlive a typical combustion engine car.
Have a look at our report on one of our recent Nissan Leafs with 120,000 miles. We have had cars here with over 160,000 miles with around 80% battery health.