An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Batteries come in many sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers.
Battery has two terminals. One terminal is marked (+), or positive, while the other is marked (-), or negative. In normal flashlight batteries, like AA, C or D cell, the terminals are located on the ends. On a 9-volt or car battery, however, the terminals are situated next to each other on the top of the unit. If you connect a wire between the two terminals, the electrons will flow from the negative end to the positive end as fast as they can. This will quickly wear out the battery and can also be dangerous, particularly on larger batteries. To properly harness the electric charge produced by a battery, you must connect it to a load. The load might be something like a light bulb, a motor or an electronic circuit like a radio.