Fourteen thermal runaway propagation experiments were conducted on a 6.6 kWh Lithium-ion pouch-cell module to investigate the effects of four different trigger methods on thermal runaway propagation. The methods were Electrical heating with two 100 W heating pads, local heating with a small 2 kW flame, overcharging (1–2 C), and heating the module with a larger 50 kW burner. Studies of thermal runaway propagation typically employ only a single trigger method throughout the experimental campaign. However, from the literature on single Lithium-ion battery cells, it is known that the trigger method significantly affects many properties of a thermal runaway, such as the maximum temperature, mass loss, and gas production rate. The present research showed that the trigger method can significantly affect propagation, so that one method may lead to propagation throughout the entire module, while another may not. The total mass loss for the Local flame and Electrical heating, which resulted in slow cell-to-cell propagation, was independent of the trigger method. However, the change in the mass loss rate over time was different. A novel method for investigating individual thermal runaway events showed that thermal feedback from external flames did not affect cell-to-cell thermal runaway propagation.