When it comes to batteries, most of us do not pay much attention to them beyond size, purpose and ability to be recharged. Everyone knows about AA, AAA and D cells, watch batteries and car batteries, but when it comes to other types, few people can distinguish their purpose and performance. The key to understanding battery ratings is to learn about and decipher their specifications.
At its most basic, a battery is anything that stores energy to be used at a later time. By this definition, even a rock pushed to the edge of a cliff can be considered a battery because the energy it took to push it to the edge is stored as potential kinetic energy, which can be released by rolling the rock down the cliff. Today, however, the term battery is reserved for a device that stores electrical energy.
The first batteries were invented by the Sumerians in 250 B.C., and it is believed they were used to electroplate metals for jewelry. Since this time, batteries have changed substantially, but they still have the same general design: two electrodes composed of different metals submerged in an electrolyte solution. The first modern battery is attributed to Alessandro Volta, and it was made of a copper electrode and a zinc electrode with an electrolyte solution of sulfuric acid mixed with water or brine.