The dynamic response of lithium-ion cells under mechanical loading is known to feature significant strain-rate effects. Opposite trends in failure strength have been observed between elliptic cells (with hard shell casing) versus pouch cells, when cells were subjected to high-speed loads. This paper elucidates the reason for the observed effects by comparing dynamic data from tests on lithium-ion cells in different configurations. It reports on new dynamic tests on cells with different form factors, thicknesses, and casings. The two basic types of cells investigated were pouch cells and elliptical cells, with and without liquid electrolyte. Additionally, the elliptical cells were tested with a hard aluminum housing and with a soft pouch covering. All the cells have been loaded by a hemispherical punch with velocities between 0.01 mm/s and 5000 mm/s. Intrusion force, depth, and velocity, as well as cell voltage were measured with high time-resolution during the experiments. A comparison of the data from different configurations allows to discriminate the effects of electrolyte, thickness, and casing on the dynamic response of the cells. One main finding is that the presence of the electrolyte has the most significant effect on the overall relative strain-rate behavior. Thickness and casing do add simple scaling factors. These findings are of great importance for battery pack design in electric vehicles.