A study of transition metal oxide cathodes to replace the iron disulfide used in thermal batteries was conducted at Saft ABSD in Cockeysville, MD. The goal was to identify cathode materials yielding higher voltage and improvements in energy density. Selected materials were evaluated versus lithium immobilized by iron powder (LAN) anodes in molten nitrate electrolytes. Single cells were tested between heated platens inside an argon atmosphere glove box over the temperature range of 240°C to 425°C. The best cathode material tested was lithiated manganese dioxide, LiMn2O4. After extensive experimentation, we were able to achieve a peak voltage of 2.8 V under a load of 200 ma/cm2 and a two-plateau voltage discharge yielding 221 Wh/kg at 260°C. This exceeds the specific energy of state-of-the-art cells with iron disulfide.