A car battery is a rechargeable power source that provides electricity to start the engine and operate electrical components in a vehicle. It stores energy in chemical form and converts it to electrical energy when needed. Most car batteries are lead-acid types, which consist of lead plates and sulfuric acid. When the engine is running, the car's alternator recharges the battery, ensuring it has enough power for future starts. A typical car battery lasts about three to five years, depending on usage and maintenance. Regular checks can help prevent unexpected failures and ensure reliable performance.