A secondary battery, also known as a rechargeable battery, is a type of battery that can be recharged and used multiple times. It functions through reversible chemical reactions, allowing it to be recharged by applying electrical energy to restore its charge. Secondary batteries are commonly used in applications where frequent battery replacement would be impractical or costly, such as in smartphones, laptops, electric vehicles, and renewable energy storage systems. Examples include lithium-ion batteries, nickel-metal hydride (NiMH) batteries, and lead-acid batteries. They are valued for their cost-effectiveness, environmental benefits, and long-term usability.