The study investigates the state-of-charge (SOC) dependence of thermal runaway (TR) in lithium-ion (Li-ion) cells and its implications on thermal runaway propagation (TRP) in battery modules. Through accelerating rate calorimetry (ARC) experiments, the researchers observed that higher SOCs lead to earlier onset temperatures, higher peak temperatures, and increased self-heating rates during TR. These characteristics are captured in a hierarchical TR model, which is validated with experimental data. The model is then used to simulate TR behavior in oven tests and analyze TRP in a 3 × 3 Li-ion battery module with uniform and imbalanced SOCs. The findings highlight the critical role of SOC variability in TRP rates and the thermal energy required to initiate TRP under abuse conditions. The proposed framework can inform the design of advanced battery thermal management systems and cooling strategies to mitigate cell-to-cell TRP.The study investigates the state-of-charge (SOC) dependence of thermal runaway (TR) in lithium-ion (Li-ion) cells and its implications on thermal runaway propagation (TRP) in battery modules. Through accelerating rate calorimetry (ARC) experiments, the researchers observed that higher SOCs lead to earlier onset temperatures, higher peak temperatures, and increased self-heating rates during TR. These characteristics are captured in a hierarchical TR model, which is validated with experimental data. The model is then used to simulate TR behavior in oven tests and analyze TRP in a 3 × 3 Li-ion battery module with uniform and imbalanced SOCs. The findings highlight the critical role of SOC variability in TRP rates and the thermal energy required to initiate TRP under abuse conditions. The proposed framework can inform the design of advanced battery thermal management systems and cooling strategies to mitigate cell-to-cell TRP.