Abstract: The mechanical properties of secondary cells are crucial to the safety and reliability of battery packs, which can fail due to extrusion and vibration in a vehicle crash. To analyze the structural response of the secondary cell and its other dynamic behaviors, the experiment and some numerical simulations were carried out based on single reference impact testing. Then, an equivalent constitutive relationship of the secondary cell was proposed to reveal the dynamic properties and used to guide the safety estimation of the battery pack. As the input parameter to the finite element model, the equivalent constitutive relationship, including but not limited to the elastic modulus and stain-stress curve, determines the simulation precision of the battery packs. Compared to the experimental results of the natural frequency of the battery pack, the simulation error is below 2% when the elastic modulus of the secondary cell in the battery pack has been verified.