In a solid-state hydrogen storage tank, the storage medium is most often in the form of an intermetallic alloy powder. With each cycle of hydrogen absorption/desorption, the particles swell, move, fragment, and segregate. Understanding and modeling these phenomena are essential in order to guide engineers during the tank design process. However, there are little data in the literature on the mechanical behavior of powders for storage applications. This study focuses on the flowability and compression behavior of an intermetallic powder, with the aim of analyzing particle mobility in a confined environment as well as the transmission of forces to the tank walls. In order to represent the evolution of particle size through fragmentation during cycles, five ${\mathrm{T}\mathrm{i}\mathrm{F}\mathrm{e}}_{\left(1-\mathrm{x}\right)}{\mathrm{M}\mathrm{n}}_{\mathrm{x}}\left(\mathrm{x}\approx 0.1\right)$ powders, differing in their average particle size and polydispersity, are studied. Flowability tests on Granutools^® (Awans, Belgium) instruments show that behaviors differ. Fine-grained samples exhibit rheo-thickening behavior, while coarser samples are quasi-Newtonian. These tests highlight variations in cohesion and internal friction, particularly for polydisperse samples. Stepwise cyclic compression tests (in stages 0-10-20-30 kN) were performed to study the elastic response of the powder under confinement and its ability to transfer stresses to the walls. This work highlights the impact of particle size and polydispersity on stress transfer in a confined space. This work therefore presents the mechanical effects of changes in particle size and polydispersity during absorption/desorption cycles on the overall behavior of the powder storage bed, in terms of flowability, cohesion, and stress transmission, in order to better understand, in the long term, its impact on tank deformation.