Ionic conductivity and electrode interface properties of solid polymer electrolytes (SPE) based on high-molecular-weight branched polyethers have been studied for their application to solid state rechargeable lithium batteries. Nigh molecular weight (10(5)-10(6)) comb-shaped polyethers, poly[ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether] [P(EO/MEEGE)], allow to give elastic and self-standing polymer electrolyte films without cross-linking. With increasing the MEEGE composition, the conductivity appreciably increases and takes a maximum at MEEGE compositions of 0.2-0.3, due to the fast ion transport assisted by highly mobile ether side-chains. Interfacial resistance (R-i) at the lithium: electrode interface decreases with increasing ionic conductivities of the polymer electrolytes, which are affected by the MEEGE composition and Lithium salt species complexed with the copolymers. An all-solid lithium polymer battery, Li/P(EO/MEEGE = 91/9)-LiClO4/LiCoO2 composite cathode cell, exhibited a discharging life of over 7 h at 0.1 mA/cm(2) and a low cell impedance of 96 Omega cm(2) after full charge at 60 degrees C.