With the rapid increase in the energy density of power batteries, ensuring their safety has attracted growing attention. In order to study the relationship between the safety of a power battery and its energy density, we adopt three typical triggering methods, i.e., penetration, overcharging and heating, to conduct thermal runaway (TR) tests on 13 groups of commercially available power batteries with different material systems and structural forms. The obtained TR behaviors are analyzed based on TR temperature, introduced energy, and TR outcome. The results show that the three methods have different probabilities of triggering TR, and the TR characteristics of the same samples can be different under different triggering modes. The higher the energy density of the battery, the lower the introduced energy required to trigger its TR. When the energy density reaches a certain level, the introduced energy threshold stabilizes.