Viscosity and ionic conductivity were carried out on gel electrolytes made of highly amorphous polymer, poly(methylmethacrylate), LiClO4 salt, and a solvent of high boiling temperature, propylene carbonate. In the composition range 0 weight % - 35 weight % of PMMA in the gel, the conductivity decreases very slightly as the amount of PMMA increases. On the other hand, a large increase of viscosity is observed. This result is interpreted on the basis that, from a microscopic point of view, the gel may be seen as a free liquid electrolyte encaged in a polymer matrix. For amounts of PMMA larger than 35 weight % the conductivity decreases more rapidly. These gels are transparent in the visible region, thermally stable in a large domain of temperatures, i.e., -65 degree(s)C, +160 degree(s)C and electrochemically stable, i.e., (Delta) V equals 4.5 V. They are good candidates as `solid electrolytes' for the realization of solid state electrochromic `smart' windows.