Thermal batteries are used in applications were high reliability is a key requirement. They can be stored for decades and activated in less than a second. Most contemporary thermal batteries use a lithium alloy anode, a halide salt eutectic electrolyte and a metal disulfide cathode. It is the cathode that we are interested in here. Three commonly used cathodes are FeS2, CoS2 and NiS2 and have all been reported to undergo different discharge pathways eventually leading to full reduction of the transition metal. However, discharge of these materials at temperature has never been observed in-situ and thus unknown phases or processes may be present. We wish to investigate these materials using a modified in-situ sample environment previously developed in a project between ISIS and the University of St Andrews in which we will discharge these thermal cells while collecting NPD patterns.