Depending on how long “several weeks” happens to be, the answer could be yes. Today’s car batteries have the ability to store energy for long periods of time, often for many weeks, before they go flat. Batteries have a natural ability to discharge due to the chemical reaction that is constantly occurring in the battery. When the car is running, there are a number of systems that need an electrical supply and the battery will run down if there is no additional charge added back by the alternator. While not running, the discharge is less but over time will cause the battery to go flat.
The type of battery you have will determine how quickly it will discharge or go flat. Premium batteries, though produced in the same way as their more-economical counterparts, have additional measures that help increase their effective life. These additional measures will also increase the amount of time you can leave the battery dormant in the car. Some cars have additional electrical drains on the battery while the car is parked, such as a car security system that may cause additional strain on the battery. If you are concerned there are too many latent systems on the car draining power, consider removing fuses to those systems instead of disconnecting the battery.
A car battery maintenance charger is relatively inexpensive and can be used to keep your car battery’s charge at a normal level for an indefinite period of time. Consider making this purchase if you plan to keep your car parked for extended periods of time. Keep in mind the location of the parked car and try to avoid allowing the charger to come into contact with excess moisture or wild animals. Using a maintenance charger will allow you to have peace of mind when parking your car for several weeks or longer.
Flat batteries can be an indicator that not only has there been an excessive drain on the system, but that it may be time for a new battery. Consider whether the battery in your car is newer or if it has been in the vehicle for several years. Older batteries will hold their charge for several days at a time, but may fail after just a week or so without the car being started. Invest a little extra money in a new battery and you should be able to leave your car parked for longer periods of time.