Thermal batteries are widely used in various weapon systems due to their advantages， such as fast activation， long storage life， and a wide operating temperature range. However， compared to short-duration thermal batteries， long-duration thermal batteries often exhibit significant capacity loss. The mechanism of capacity loss in long-duration lithium-boron thermal batteries is investigated. The findings indicate that cathode materials with high thermal stability benefit performance during both high- and low-temperature discharges. However， mature thermal battery cathodes currently cannot withstand thermal shock. The dissolution and diffusion of the anode are identified as key factors contributing to the capacity loss. Improvement measures to address these issues are proposed.