The main features of cyclic voltammograms (CVs) of thin electrochromic films based on a-WO 3 were investigated. First, the chemical capacitance is defined in terms of the electrochemical potential variation with the insertion level, x, and is measured under galvanostatic (chronopotentiometry) quasi-equilibrium conditions. An equilibrium capacitance increasing rapidly with respect to insertion level or negative potential is observed, respectively C c h ≃x a at x>10 - 3 (a~0.74) and C c h ≃V α (α~3). Simulation methods used to generate the observed CVs are described in detail. Major CV peaks can be simply understood as charging and discharging of the variable capacitor, in conjunction with a distortion of the voltage scale due to a series transport process. Therefore a simple RC equivalent circuit allows us to explain the principal CVs characteristics of lithium intercalation and deintercalation in amorphous films.