J1772 is already pretty much a universal charging standard.I'm asking because I was wondering why a recharging station couldn't simply spin the rear tires (like a dynamometer) to use the car's built-in system to top off the battery. Could be a universal charging station for any EV with regen.
To answer your original question, it's pretty inefficient (but better than wasting it).
I think around 30-50%.
That's why if you're doing serious hypermiling (Australian outback), you're actually better off with regen set to 'Low'.
Going downhill it's more efficient to just roll faster than to hold your speed while charging batteries.
That's precisely what I'm saying.Driving in a way where you never need regen would be the most efficient