High-voltage, large-capacity storage batteries are used for the back-up power source of, for example, the telephone switchboard and the computer, the power source for emergency lighting, and to meet rising necessity for the leveling of power demand. Various kinds of large-capacity secondary batteries have been used, including nickel-cadmium batteries, nickel-metal hydride batteries, lithium batteries and sodium-sulfur batteries. Secondary or storage batteries are made up of an electrochemical cell or cells that generate electricity. Rechargeable storage batteries can be recharged by passing a current through them in the reverse direction. The voltage or force generated by the recharging process depends on the number of cells that make up the battery. Lead-acid cell are used to start the internal combustion engines of cars, trucks, motorcycles, lawn and garden equipment. And the nickel-cadmium cell used in various portable electronic devices. The nickel-metal hydride storage battery has recently been used as an electric source for electric vehicles, hybrid electric vehicles, electric bicycles, and power tools.
