The electrochemical charging of Pd rods by deuterium involves a complex coupling of electrochemical, interfacial and transport processes. In order to predict the overpotential, surface coverage and bulk loading of the electrode during charging, a model has been developed that incorporates the essential features of these processes and involves variables such as the electrochemical rate constants, the bulk diffusion coefficient and the charging current. Features of the computed time dependence of the bulk loading are then compared with published experimental charging curves. New microscopic observations and X-ray diffraction data provide further evidence for the details of the charging process.