Design studies carried out on 20-30 kWh zinc-bromine electric vehicle battery systems project energy densities of 65-70 Wh/kg and 80-85 Wh/l. Zinc bromine concentration and zinc electrode loading are the key variables which determine energy density. Power density, projected to be 90-100 W/kg, is primarily a function of electrolyte conductivity, since cell polarization studies show very little concentration or activation polarization.A four cell Zn-Br2 stack ( 250 Wh) has been tested under the SAE J227aD driving schedule as negotiated by the DOE/GE/Chrysler electric vehicle (ETV-l). Test data indicate the need for conductivity additives to the electrolyte to achieve the necessary power densities. Using KCl and other conductivity additives, vehicle ranges of 95-100 miles can be projected with the use of regenerative braking. Charge acceptance during regenerative braking is very good (∼100%) and results in an improvement in vehicle range of 25%.