Just to make a subtle clarification, while it is true that an EV's battery will degrade over time, it's mainly a loss of capacity rather than a loss of efficiency. A battery at 80% of its original capacity will cost 80% of what it originally cost to charge to full, because you're putting less energy into it. The range is reduced, but the cost per mile driven isn't really different.

Technically, a degraded battery's internal resistance will have increased from when it was new, but it's a relatively modest change. The increase in resistive losses would be hard to notice compared to major losses like aerodynamics.