To maintain the battery of your Volkswagen, you should check the battery terminals and cables for corrosion, clean any dirt or debris off the terminals, and check the electrolyte level if it is a wet battery. If necessary, use a voltmeter to test the voltage of the battery. Check the water level of the battery periodically and top it up with distilled water, as needed. Additionally, it is important to ensure that the battery is recharged often, and that the charge is maintained for optimal performance.