The invention is an electrochemical battery cell, such as a Li/FeS<SUB>2 </SUB>cell, with a nonaqueous liquid electrolyte having a solvent with a high ether content and a solute including LiI and one or more additional salts, preferably LiCF<SUB>3</SUB>SO<SUB>3</SUB>, that can avoid a sharp drop in voltage on high rate and high power discharge at low temperatures, while still providing reasonable capacity on high rate and high power discharge at room temperature. The electrolyte solvent includes 1,3-dioxolane and 1,2-dimethoxyethan in a volume ratio greater than 45:55 and less than 85:15. When the total solute concentration in the electrolyte is low (0.40 to 0.65 mol/l solvent), the solute contains at least 35 mole percent LiI, and when the total solute concentration in the electrolyte is high (greater than 0.65 to 2.0 mol/l solvent), the solute contains less than 35 mole percent LiI. |