  We study the equal area law and charge-electric potential criticality for the
charged Anti-de Sitter black holes. Considering that the black hole charge is a
double-valued function of the electric potential, we investigate the equal area
law in detail. We find that the equal area law has two different expressions
when the thermodynamic quantities are near the critical point and far from the
critical point. For these two different cases, we obtain the analytical
coexistence curve for the low and high electric potential black hole phases by
using these two expressions of the equal area law. Based on the result, we
analytically study the phase diagram and the critical phenomena in the
charge-electric potential plane.
