The primary function of your car battery is to start your vehicle. It's also in charge of supplying power to your vehicle's lighting, audio system, and any other electrically powered components.

That depends on the type of battery. The better modern batteries, particularly AGM batteries like the Optima, are sealed and require very little maintenance. If they aren't used regularly, all you need to do is connect them to a suitable voltage maintainer. If you have a more classic flooded cell battery, simply check the water level from time to time to prevent it from drying out and exposing the plates.