And we don't really know the lifespan of batteries. I've heard that early Leafs have lost significant range, but I'd love to be corrected on that. Tesla charges me $600 per year for the annual maintenance on my Roadster, and that far exceeds what I'd spend on gas if I drove the Prius instead. (I still hate driving the Prius because I don't like burning gas.)
Leafs don't have a proper battery temperature management system. It's like saying you have to replace video cards in a computer every 3 months because this one manufacturer decided to skimp out on a proper fan. You're thinking that the battery technology used in cell phones is the same tech used in EVs--this is not at all the case.
We actually do know how batteries last long-term:
1) Volt batteries are in the 7+ year old mark, and their degradation is remarkably low.
2) Tesla batteries are in the 200k+ mile mark, and their degradation is remarkably low. (Tesloop battery degraded 8% in 200k miles in a desert climate with 2x daily supercharging--ultimate stressful conditions)
3) 7+ year old Leaf batteries do remarkably well, if the Leaf is driven in a cool country (which again, is a design flaw and not a flaw with battery technology in general). See Leaf taxis with 130k+ miles in the UK that undergo constant fast charging.
By the time you have to replace an out of warranty battery--which, again, is
eight years in the future with a Tesla--battery costs will be half of what they are at the time of purchase.
The average US gas car doesn't last 8 years--it starts becoming more expensive to own/repair/maintain than selling the car and buying brand new.
The average EV still has almost no maintenance to speak of after 8 years. Do some research--econo-EVs like Leafs and Bolts have next to zero maintenance costs. In eight years, a Model 3 battery could very easily cost <3-4k even assuming it suddenly dies at the eight year and one day mark.
Here's the bottom line: electric drivetrains, to most informed individuals out there, is the single most premium feature out there. The electric drivetrain makes the slowest Model 3 out-accelerate luxury gas cars twice their cost, and destroy any similarly-priced gas car on the market. The electric drivetrain saves most drivers dozens of hours a year from wasting their lives at gas stations. It is quieter than the quietest luxury cars; it is smoother than million dollar gas cars.
This is the reason why the Model S destroys all of its luxury competition in the US, despite having the interior luxury of a $35k gas car. This is the reason why the Model 3 will be the best car you can buy for $35k, despite it having the interior luxury of a well-equipped Civic. This is the reason why crappy, cars-on-a-leash like the Leaf and Spark out-perform all comparable gas cars on owner satisfaction despite having a 60 mile range in the wintertime.
This same argument happened with the smartphone revolution. Unlike the smartphone revolution, EVs already cost less than similarly-priced gas cars over the course of a loan, and will soon cost less up-front than similarly-equipped gas cars. People will pay for better and simple (as evidenced by the number of people dropping $800 every two years on smartphones), and EVs are no different.