Battery systems are devices that store electrical energy for later use. They consist of one or more batteries, which are made up of electrochemical cells that convert chemical energy into electrical energy. These systems are commonly used in various applications, including electric vehicles, portable electronics, and renewable energy storage. The performance of battery systems is measured by their capacity, which indicates how much energy they can store, and their voltage, which determines the electrical potential. Different types of batteries, such as lithium-ion and lead-acid, have unique characteristics that make them suitable for specific uses, balancing factors like cost, weight, and lifespan.