Batteries are the heart of a car's electrical system, giving it the initial jolt to start and then continuously powering its features. They come in various types, with lead-acid batteries being the most affordable, while AGM batteries last longer and lithium-ion offer the most power but cost the most. Cold Cranking Amps (CCA) show a battery's cold weather starting ability, and Reserve Capacity (RC) indicates how long it can power the car without the alternator.