Put more succinctly: Regenerative braking has < 100% round trip efficiency, so repeatedly speeding up and slowing down hurts gas mileage. The driver thought i

Put more succinctly: Regenerative braking has < 100% round trip efficiency, so repeatedly speeding up and slowing down hurts gas mileage. The driver thought it had > 100% efficiency. If that were the case, then the car would be a perpetual motion machine, and they’d save a ton on gas.