Battery replacement isn't much of a concern if you buy a properly designed car. I only have experience with my volt in relatively cold temps, but I regularly get 31 to 35 miles in 25 to 50F weather and mostly highway on battery. This car has 90k miles on it and probably 30k of which were powered from the battery.
So, no battery degradation to speak of.
Nissan Leaf is quite possibly the exact opposite.
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