It is basic physic. There is all the time friction of air and the road. You can never recover that. And in rare cases where you actually can recover energy, a

It is basic physic. There is all the time friction of air and the road. You can never recover that. And in rare cases where you actually can recover energy, at non emergency slowing down, it is probably indeed in that ballpark, wich is something(especially in city with stop and go), but not very high or much. With very high tech, you can increase that number a bit, but not worth the effort. Electric cars need good batteries and every improvement there is good.