for a battery that is de -energizing or discharging, the voltage across its terminal Vterm will be less than its emf E . Vterm= E-Ir where I is the current through the battery and R is its internal resistance.

connect a single battery. with a resistor of 220 ohm. the emf (or open circuit voltage) of the battery is given on its outer jacket to be 1.5 volts. the resistance decade box will provide the 220 Ohn resistance.