The primary function of a car battery is to supply electrical energy to the starter motor, which turns the engine over and gets it running. Once the engine is running, the alternator takes over and provides electrical power to the car's systems while also recharging the battery.

Car batteries are typically lead-acid batteries. They consist of a plastic case containing cells filled with a mixture of sulfuric acid and water (electrolyte), lead plates (positive and negative electrodes), and separators that keep the plates from touching each other.

A typical car battery provides 12 volts of direct current (DC). The capacity of a battery is measured in ampere-hours (Ah) or reserve capacity (RC), indicating how much charge it can store and how long it can provide power before needing to be recharged.

Most modern car batteries are maintenance-free, meaning they are sealed and do not require adding water or checking electrolyte levels. However, it's still important to keep the battery terminals clean and free from corrosion to ensure a good electrical connection.

Car batteries are recharged by the vehicle's alternator while the engine is running. The alternator converts mechanical energy from the engine into electrical energy to both power the car's electrical systems and recharge the battery. Over time, batteries can lose their ability to hold a charge and may need to be replaced.

The lifespan of a car battery varies depending on factors such as climate, driving habits, and maintenance. On average, a car battery may last 3 to 5 years. Signs of a failing battery include difficulty starting the engine, dim headlights, and a check battery light on the dashboard.

It's important to dispose of old car batteries properly because they contain hazardous materials such as lead and sulfuric acid. Many auto parts stores and recycling centers accept old car batteries for recycling.