Optimum speed is around 40 mph. Drag varies as the square of speed.
So not ideal for motorway though goodfor 83 *mph.
You might get 20 miles at that speed, maybe not.

What's the heater like when its rather cold like now?..
--
Tony Sayer

Heater works fine. But best to pre-heat it whilst it's plugged in on
charge..

So in reality then not a lot of cop when you need it most;...
--
Tony Sayer