The open circuit voltage (OCV) of a battery depends on the electrochemical system selected for it and is somewhat affected by the electrolyte concentration, degree of discharge of the battery, temperature, and other factors. Once these parameters have been fixed, the OCV then is a fairly reproducible quantity. Both the ampere‐hour capacity and the watt‐hour energy of a storage battery are referred to one complete discharge of the battery after it has been charged to full capacity. Current density serves as a measure of the relative reaction rate. Therefore, plots of voltage against current density provide a useful characterization of a battery reflecting its specific properties independent of its size. Battery characteristics strongly depend on the operating temperature. As a rule, both the discharge voltage and the reactant utilization coefficient are lower at lower temperatures.