Most modern vehicles have an insulating jacket around the battery to give it a degree of protection from the cold.
Assuming the car is 'fairly' modern, the integrated alarm/immobiliser will place a constant load on the battery - that's likely going to be the greatest source of drain. In the real world it should be possible to park a car for a couple of weeks without the battery becoming drained to the extent that the car can't be started. If you find that it doesn't last that long, it may well be a sign that the battery should be replaced - failure to hold charge in the cold being a warning sign ....however, it's also possible that that's a fault in the vehicle. I experienced a battery discharge problem in an E39 BMW 5 series a few years ago - turned out to be a faulty temperature control device in the heating system, which caused the ventilation fans to run at random while the vehicle was parked - cured the problem by replacing what is referred to as the 'hedgehog'.
