http://www.wikihow.com/Store-a-Car
8 Use a battery maintainer if the car will be stored for more than a month. These are basically "smart" battery chargers that only turn on periodically. For short times, a few months, the maintainer can be attached to the battery while still in the car. For extended periods, if you are comfortable with basic mechanics, removing the battery and attaching the maintainer to it outside the car is a advisable. If you choose to do this, be sure to contact the car's manufacturer to ensure that this will not confuse the on-board computers, and that you have written down any needed access codes for devices such as the stereo or alarm.
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