This chapter focuses on the operation and control of batteries in off-grid systems, emphasizing efficient charging, discharging, and overall management. It provides a detailed overview of the three-stage charging process for lead–acid batteries, comprising bulk, absorption, and float stages, and explains battery discharge control through low-voltage disconnection mechanisms. The chapter also addresses the unique requirements of lithium-ion batteries, highlighting the role and functionality of battery management systems. Additionally, it develops circuit models for analyzing current in off-grid systems featuring multiple energy sources, charge controllers, diversion load controllers, and loads connected to the DC bus. Finally, the chapter examines the algorithms employed in maximum power point trackers (MPPT) to optimize the performance of solar photovoltaic systems.