The thermodynamics and kinetics of silver stoichiometry change in RbAg4I5:graphite composites briefly reported in a previous contribution are treated in detail. The stoichiometric variations occurring at the interface are achieved electrochemically and chemically. In samples that are not deliberately compacted samples, Stranski-Krastanov wetting of RbAg4I5 on carbon enables measurement of heterogeneous ambipolar Ag diffusion along the interface. If samples are deliberated compacted, the interfacial storage occurs through supercapacitive charging through the bulk path. The application of composites as electrodes in supercapacitor or battery mode underscores the very fast kinetics.