Batteries and fuel cells (FCs) are the two major types of solar energy storage devices currently in use. Secondary batteries reversibly convert stored chemical energy (e.g., from solar power devices) into electrical energy. FCs generally convert chemical energy from fuel into electricity via chemical reactions with oxygen. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and methanol are sometimes used. FCs are distinct from batteries in that the former require a constant source of fuel and oxygen (e.g., through solar electrolysis of water) to sustain their chemical reactions, and can continuously produce electricity for as long as these inputs are supplied. A system consisting of stored hydrogen in a cylinder tank and an FC system functions as a battery. In this chapter, we discuss batteries and FCs for use with solar power devices, in terms of current practice and future perspectives.