A simple battery model established by Denno [Power system design and applications for alternative energy sources, Englewood Cliffs, NJ: Prentice-Hall: 1989] is used to investigate the basic question of how to maximize the work output of an electric battery. The discharge time is determined reasonably and the load resistance is matched optimally. The results obtained here can be used to explain quantitatively the example given by Gyftopoulos [Energy 24 (1999) 1035].