For efficient storage of hydrogen (H) in solids, not only the choice of materials is important but also the lattice defects involved play an essential role especially for the kinetics of absorption/desorption of H at a given temperature. For example, in the system Mg-X-H (X stands for a metallic constituent) which is highly relevant for commercial applications, free-volume defects act as trapping sites for H which, however, have to be stable against thermal loads if a high reproducibility in H-storage characteristics is required. This stabilization can be achieved by constituents like Zn and Zr in Mg (alloy ZK60), or by H itself according to recent studies in ECAP- and CR-processed Pd. The current presentation reports systematic studies of differently HPT-processed Pd-H materials starting with different H-concentrations, and identified mainly vacancy-type defects to be stabilized by the H-atoms especially at severe plastic deformations, and only very few dislocations and grain boundaries. The results have been confirmed by isochronal microhardness measurements showing distinct anneal hardening effects connected with H-mediated vacancy agglomeration, and no ones associated with H-stabilized dislocations and/or grain boundaries, respectively. Recently, it has been found that the stable defects also in case of Mg-X-H system mainly consist of vacancies, and not of dislocations.