Depending on weather, how you drive it (speed, uphill then downhill or downhill then uphill), and what tires are on it, 64 miles might not be unreasonable. During the winter I was getting about 66 miles on a full charge.
What might concern me is your statement that the battery drains really fast when it sits there. Generally the car should hold a charge for a long time when it is just sitting there, plugged in or not. Is the car in extreme weather conditions so that it has to heat or cool the battery? Did you accidentally leave it turned on? I think that the car will turn off automatically after a period of time, but I haven't tested that. I don't think the car uses much energy when turned on and not moving, but it might affect the range reading.
2015 Spark EV 1LT, DCFC