Publisher Summary This chapter discusses various types of metal—air batteries: zinc-air primary batteries, metal-air secondary batteries, and aluminum-air secondary batteries. Zinc-air batteries are used for many years, but their use has been restricted to very low-rate applications. As a result of the work performed on fuel cells and advancements in technology for making thin gas electrodes that operate at high current densities, zinc-air cells are now being examined as a power source.