Many off-grid electrical systems in developing countries use energy storage to increase their reliability and operational flexibility. The primary goals of this chapter are to provide nonspecialists with an understanding of the basic electrochemistry occurring in chemical batteries and to describe the operation and performance of batteries from an electrical viewpoint. Particular attention is given to interpreting specifications provided by battery manufacturers. A circuit model of a chemical battery is developed. It is used in subsequent chapters to analyze the operation of off-grid systems. The chapter considers flooded, absorbent glass mat (AGM), gel, and LiFePO \(_4\) lithium–ion batteries. Safety and maintenance aspects are covered. Economic, environmental, and social considerations of the use of batteries in off-grid electrification are discussed.