These days the batteries go down really fast. With the cold, heating up the inside of the car takes a lot of it. Also driving in electric when is cold uses a higer % of the battery. Just an example, tried to preheat the car only using the battery (unplugged) when the temperature outside was 2C and the battery went down to 79%.
Some advice, try to preheat the car, plugged, before taking it. That way it wont have to heat it while you are driving and it also warms up the batteries.