Thermal batteries find use in applications such as emergency power systems and ejector seats in aircraft. They operate at elevated temperatures of around 400-500 °C, where the halide salt electrolyte is molten. There is considerable lack of detailed understanding of the structure-property relationships in these materials, due to the high temperature required and sealed battery cells involved in such measurements. We are currently undertaking a project to understand how the chemical structure of the cathode materials changes on discharge of the battery. Here, we aim to look at the in-situ battery discharge of three cathode materials, using a specialist rig which has been developed at St Andrews, to collect electrochemical and diffraction data simultaneously.