A battery (see schematic below) is an electrochemical device that converts chemical energy into electricity, by use of a galvanic cell. A galvanic cell is a fairly simple device consisting of two electrodes (an anode and a cathode) and an electrolyte solution. Batteries consist of one or more galvanic cells.

  A battery is an electrical storage device. As the chemical compositions in the battery change, electrical energy is stored or released. In rechargeable batteries this process can be repeated many times. Batteries are not 100% efficient - some energy is lost as heat when charging and discharging. If you use 1000 watts from a battery, it might take 1200 watts or more to fully recharge it. Slower charging and discharging rates are more efficient. A battery rated at 180 Amp-hours over 6 hours might be rated at 220 Amp-hour at the 20-hour rate, and 260 Amp-hours at the 48-hour rate. Typical efficiency in a lead-acid battery is 85-95%, in alkaline and Nickel-Cad battery it is about 65%.  

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