The Apollo Command Module's primary source of electric power was from a set of three "fuel cells" housed in the Service Module. Each fuel cell combines hydrogen and oxygen to produce electricity and water. The water was used for drinking by the astronaut crew. Each of the fuel cell power plants contain 31 separate cells connected in series. Each cell has hydrogen and an oxygen compartments and electrodes and in combination produce 27 to 31 volts. Normal power output for each power plant is 563 to 1420 watts, with a maximum of 2300 watts.

This particular fuel cell, made by United Aircraft Corporation, was intended for use in the Apollo Service Module 115/115A, which was scheduled for use during the Skylab Program. SM115 was never flown and these unused fuel cells were offered to the Smithsonian in 1977.