Solid‐state electrochemical cells have been devised using a variety of metals as anodes and electronically conducting charge‐transfer complexes as cathodes. The product of the electrochemical reaction, the electrolyte, was formed in situ. Data are reported for halogen complexes as well as for complexes containing nitrogen compounds as acceptors. It is shown that the voltage ‐producing electrochemical reaction is the formation of the corresponding metal salt. Open‐circuit voltages of 1.5–2.5v per cell were attained with magnesium or calcium anodes, and short‐circuit current densities of up to 25 ma/cm2 were found. Current‐voltage characteristics have been studied as a function of temperature, and constant‐load discharge curves are shown. Maximum power densities of one watt per pound and useful energy densities of 1 whr/lb are reported. An analysis based on irreversible thermodynamics is presented, and possible applications are suggested.