The electromotive force is the difference between the equilibrium electrode potentials of the two electrodes. Taking a lead-acid battery as an example, E=Ф+0-Ф-0+RT/F*In(αH2SO4/αH2O). (HHR-210AB18F4)
Where: E-electromotive force
Ф+0—positive standard electrode potential, which is 1.690V
Ф-0—Negative standard electrode potential, which is -0.356V
R—general gas constant, which is 8.314
T—temperature, related to the temperature at which the battery is placed
F—Faraday constant, the value is 96485
αH2SO4—the activity of sulfuric acid, related to the concentration of sulfuric acid
αH2O—the activity of water, related to the concentration of sulfuric acid
As can be seen from the above formula, the standard electromotive force of the lead-acid battery is 1.690-(-0.0.356)=2.046V, so the nominal voltage of the battery is 2V. The electromotive force of a lead-acid battery is related to temperature and sulfuric acid concentration.