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Batteries are used everywhere today including in very non-obvious places such as in buildings within emergency lighting in exit signs in buildings all over the world. The development of batteries commenced around 1800 with Alessandro Volta inventing the Voltaic pile. Volta was an Italian Physicist who made a large pile of pairs of alternating metal plates of zinc and silver (electrodes) separated by cardboard soaked in brine (electrolyte). When he connected the top and bottom contacts by a wire an electric current flowed through the wire and the voltaic pile. Measuring the electro-force that is now measured as volts was named after him. Put simply batteries work on the basis of converting chemical energy into electrical energy.
Most consumer batteries around the world have two terminals one being positive and one being negative and come as consumer batteries such as AAA or AA batteries. Industrial grade rechargeable batteries such as NiCd batteries are much more complex and more expensive. Rechargeable batteries are batteries that can be reused and this occurs by the process of having the chemical reactions reversed through the supply of electrical energy to the battery cell. This recharging restores the original integrity of the battery and hence allows the battery to be reused. However no system is perfect and the number of times a battery can be recharged depends on the degradation of the active materials and hence the loss of the electrolytes. Also corrosion will occur and this will also degrade the battery.
In Nickel-Cadmium (NiCd) batteries electrodes are made of nickel-hydroxide and cadmium. Potassium-hydroxide is the electrolyte. NiCd batteries will usually deliver a high current and can be charged in short time with a high current. NiCd batteries can suffer from memory-effect. When a NiCd battery is charged without being completely discharged, crystals grow in the battery. These crystals diminish the capacity of the battery and are difficult to remove. Hence it is important to get high quality NiCd batteries if you are using them in devices such as emergency lights.
Nickel-metal hydride (NiMH) batteries are replacing nickel-cadmium as they offer similar properties but don't suffer from the memory effect that can effect nickel-cadmiums. Both nickel-cadmium and nickel-metal hydride batteries output 1.2 volts. All rechargeable batteries lose their charge due to self-discharge. For example when not in use, nickel metal hydride batteries will lose 20% to 50% of their charge within six months due to self]discharge. Factors such as storage temperature can impact the self discharge rate. Lithium-ion (Li-ion) batteries use lithium and carbon with an electrolyte. They have a very good power-to-weight ratio and fairly slow self-discharge rates when not in use, so they are often used in high-end laptop computers and cell phones
