A ~60kW load dump resistor which is mixed into the regen circuit for when the regen is limited due to cold weather or full battery -- this would give consistent performance regardless of battery state or external temperature. Coolant could be pumped through, recycling its heat into HVAC, improving efficiency. From another thread -- regen disabled at 5°F even with 75% charged battery: http://www.teslamotorsclub.com/showthread.php/25825-Really-cold-tomorrow?p=542164&viewfull=1#post542164 If min BEMF of motor is 350V @ 60kW such a resistor would be on the order of 2 ohms. Braking resistors like this exist: http://www.reo-usa.com/docs/drives/BWD-158.pdf Continuous power would probably not exceed a few kW so cooling should not be an issue. Doubt will see this on an S/X but hope to see it integrated into GenIII platform of some kind. As an aside the VOLT uses a mix between friction brakes and regen braking (to provide consistent braking experience, as they claim), with friction used whenever regen is unavailable, but this has the disadvantage of shortening the very long brake life the S has.