To investigate the effect of different states of charge (SOC) on the thermal runaway (TR) propagation behaviors within lithium-ion-batteries based energy storage modules, an experimental setup was developed to conduct failure propagation tests on battery modules at an SOC of 97%, 85%, and 50%. The result indicates that an increase in the SOC of batteries can decrease the TR trigger temperature, making batteries trigger TR earlier and reducing the average failure propagation time between two adjacent cells. In addition, the failure propagation tests reveal that at higher SOCs, the TR reaction becomes more violent, the maximal reaction temperature is also much higher, and the damage to the battery module is severe. Compared to the battery module with 97% SOC, the TR trigger time of the battery module with 50% SOC was postponed by approximately 57.8%. Meanwhile, the average failure propagation time got prolonged by approximately 36.0%. Thus, this study can provide references for the thermal safety design of energy-storage battery modules.