A combination of one or more electrochemical Galvanic cells which store chemical energy.
History of the battery
The first battery to be created as we know of yet is the Baghdad Battery. It was made at around 100 BC. They produced such low voltage that we still do not know what they were used for.
The next set of batteries were not invented untill 1800 by Alessandro Volta. Although it was a great experimentation, it was extremely large and impractical. Batteries have been improving ever since his initial design though.
Batteries have become a common use as an easy, small, container of energy. Although the battery does not leave a large carbon footprint in the environment like fossil fuels, when thrown away carelessly they cause harmful chemicals to leak into the environment.