In the late 1880s to 1890s there was a battle going on known as the “War of the Currents.” The fight was impassioned, as it would set the stage for the electrical grid in the U.S.
The debate was about whether the U.S. electrical grid should be Alternating Current (AC) or Direct Current (DC). Each had its benefits and shortcomings. AC alternates, or reverses, the current flow periodically as it is transported and can handle high voltages over long distances with low energy loss. DC provides constant voltage or current, but typically cannot be easily converted to high voltage. DC power is often provided by a battery or can be made by transforming/rectifying AC to DC.