The EV would control the regenerative braking based on speed, same as when driving. Would not have a provision to coordinate with the MH brakes. Eventually the battery would fill and the regeneration would be reduced to zero to protect the battery. As said virtually no EV is rated to be pulled four down.
Yes if the EV could be towed four down and coordinate braking with the MH it would be a wonderful system. Could potentially fill the battery from just stopping or controlling speed down a hill.
Elon, are you reading this?
