Batteries is the academic field dedicated to the study, design, and application of electrochemical systems capable of storing and releasing electrical energy through reversible chemical reactions. This field investigates the fundamental principles governing energy conversion and storage in such devices, focusing on the materials science of electrodes and electrolytes, cell architecture, performance metrics like energy and power density, cycle life, and safety, as well as degradation mechanisms. Its significance lies in enabling portable electronics, electric mobility, grid-scale energy storage, and the effective integration of intermittent renewable energy sources.