Publisher Summary This chapter discusses numerous types of nickel batteries, such as nickel-cadmium secondary batteries, nickel-hydrogen and silver-hydrogen secondary batteries, and sodium-nickel chloride secondary batteries. There are two types of nickel-cadmium batteries: sealed and open. Both sealed and open nickel-cadmium batteries are based on similar chemical reactions. The sealed type is designed to be maintenance free and under normal conditions will not release gas, whereas an open battery is designed to release gases when necessary, and requires topping up and, in some cases, a complete electrolyte change. The basic nickel-hydrogen system consists of a catalytic gas electrode (negative) coupled with a nickel electrode (positive). These cells use a nickel positive electrode that is similar to those used on aerospace nickel-cadmium cells. The nickel-zinc secondary batteries comprise a positive nickel electrode of the sintered or pasted type similar to that used in the nickel-cadmium battery. The zinc electrode is usually prepared from powdered zinc oxide, often mixed with a Teflon binder, and pressed on to an expanded silver grid. Sodium-nickel chloride secondary battery is a relatively new type of rechargeable battery operating at 200-300°C with an emf of about 2.6V at operating temperatures and with possibilities for electric vehicle propulsion.