It literally makes no difference in efficiency unless you drive differently. Slower acceleration is a bit more efficient, but its really not a big deal generally. If the battery is warm, accelerating at halfish throttle is a very minor impact over accelerating super slow. Full throttle, and a bit near full, is definitely less efficient. But it only makes a difference for the few seconds you're accelerating. If you're constantly accelerating full throttle and then stopping, its going to be very noticeable. However, if you accelerate only occasionally and are mostly just cruising, it makes very little difference to the total trip.