With cars that are not going to be used for a long time, it would be recommended to disconnect the battery (at the terminals) from the car. This will help preserve the charge of the battery when you will use the car again.

If you don't like that, you have to at least start and warm up the engine once a week or so. This will help charge the battery and keep the rest of the engine in running condition by circulating the oil and other fluids.