Thermal battery cells utilizing molten as an oxidizing electrolyte with calcium anodes have been characterized for high rate discharge conditions. The presence of small amounts of greatly improves the cathode reaction. Half‐cell studies of anode characteristics show little variation of anode potential with temperature. Gassing at the anode‐electrolyte interface increases with temperature and current density. Overall anode consumption rates increase with increasing temperature, while anode coulombic efficiencies drop at high rates of discharge (300 mA/cm−2). Cathode half‐cell data reveal that high rate reduction of dissolved in yields masses of dendritic growth at low temperatures (260°–275°C) while at higher temperatures (> 400°C) correspondingly fewer dendritic structures are observed. Cell experiments show anticipated current‐voltage‐temperature relationships, effectively mirroring half‐cell experiments. Cell voltages sustain over 2V at 75 mA/cm−2 for periods which vary according to temperature of discharge.