It probably would not pay off for you, if you keep cars a long time.
Right now, batteries are expected to last in the 10 year range, but that's gonna be dependent on use, charge, and weather year round in your area.
And when you need to change the battery, you'll need to change the car b/c the car won't be worth enough to make the battery change worth it (thus, why electric cars are still so destructive to the environment b/c they are disposable cars in full - they won't reach the average 11.5 years for cars driven on the road)...