But Tesla explicitly says that even while they recommend it, you don't have to plug in over night: "The Model S battery will not lose a significant amount of charge when parked for long periods of time. For example, Model S owners can park at the airport without plugging in." And that the temperature make no difference: "Model S is engineered to perform in both hot and cold climates." (http://www.teslamotors.com/models/facts)
