I have a friend with a Nissan Leaf - heating it does indeed make quite an impact on the range. You can mitigate it a bit by having it preheat while still connected to the mains (there is a remote control app for your phone). His model seems a bit daft in that it uses an electrical resistance heater to heat water, which is then circulated through a conventional car style heating system. In fact it seems to pre heat the water even during the summer when its not needed. Later models apparently now include a heat pump style heater which takes less power.