I have driven Piuses/Prïï a few times, and had regen braking simply go off going down a long hill as the battery was already full. Had to use mechanical brakes to keep the speed in check. Those cars also have a "B" mode on the transmission selector to engage ICE compression braking, which I could have used. What happens if your battery is packed to the brim with electrons? Will regen braking go bye-bye when lifting off the go-fast pedal? Does the car smoothly transition to let you know what is happening?