The battery lasts about 400,000 miles.
Like heck they do. Most manufacturers seem to offer a 7-ish year "lifespan" and expect 10 - 12,000 miles a year.
For example, Nissan offers an 8-year, 100,000 mile (whichever occurs first) "Lithium-Ion Battery gradual capacity loss coverage" warranty on their higher capacity battery, but only 5-year, 60,000 miles on the lower capacity one:
The Nissan LEAF & eNV200 lithium-ion battery state of health guarantee protects against battery capacity loss (less than 9 bars out of 12) as shown on the in vehicle capacity gauge for a period of 8 years / 100,000 miles* for 40 kWh vehicles and 8 years / 100,000 miles* for 30 kWh vehicles and 5 years / 60,000 miles* for 24kWh vehicles. For LEAF flex customers, the battery state of health guarantee applies for the duration of the battery lease.
Their battery leasing programme has severe restrictions on mileage - probably based on the above, where 100,000 miles over 8 years comes to 12,500 miles a year. I did around 24,000 miles last year, though it's likely to be slightly lower from now on.
I am very tempted by an electric vehicle for my 90 mile a day (mostly) motorway commute, but until recently none of the more affordable cars could guarantee a 90 mile range in the winter with the heating, lights and wipers on, particularly towards the end of the warranty period as the battery approaches 75% capacity