Lithium insertion into amorphous thin films of tungsten trioxide (a-WO3) prepared by thermal vacuum evaporation of WO3 powder has been studied experimentally by chronoamperometry, cyclic voltammetry and ac impedance spectroscopy associated with electrochemical quartz crystal microbalance (EQCM). During cathodic polarization of the electrode and at short times two antagonistic processes occur. One is a non faradaic process and is associated with the expulsion of anions from the electrode surface under the effect of the electric field built in the electrolyte when a potential difference is imposed between the electrodes. The other one is the faradaic insertion of non-solvated lithium ions into the oxide. These two processes occur simultaneously. Under application of a cathodic overvoltage the former one leads to a loss of mass of the electrode and the latter one to a gain of mass. These two processes may explain the experimental data. From these data the diffusion coefficient of lithium ions into the oxide is determined and it is shown that it varies as insertion proceeds. A thermodynamic study of lithium insertion into a-WO3 is also performed to solve the equations of the theoretical model proposed in Part I of this paper. This thermodynamic study allowed us to determine the repulsive and/or attractive interactions between the inserted species and the host matrix as insertion occurs and the influence of the electronic term on the potential.