The terminal voltage of the battery in the open state is called the open circuit voltage. The open circuit voltage of the battery is equal to the difference between the positive electrode potential of the battery and the electrode potential of the negative electrode when the battery is open (ie, when no current flows through the two poles). The open circuit voltage of the battery is expressed by V, that is, V on = Ф + - Ф -, where Ф +, Ф - are the positive and negative electrode potentials of the battery, respectively. The open circuit voltage of a battery is generally less than its electromotive force. This is because the electrode potential established by the two poles of the battery in the electrolyte solution is usually not the equilibrium electrode potential but the stable electrode potential. Generally, it can be approximated that the open circuit voltage of the battery is the electromotive force of the battery.
