Various mixtures of quaternary ammonium bromides, QBr, have been tested for use in zinc-bromine cell electrolytes. The resultant electrolyte, modified electrolyte (MOD), allowed the Zn-Br-2 cell to operate in the temperature range 5-50 degrees C without solid phase formation. Several properties of MOD electrolyte as resistivities, bromine distributions and diffusion coefficients were studied at different temperatures. The MOD electrolyte was found superior to other electrolytes commonly used in zinc-bromine cells.