This paper presents a numerical estimation of spacecraft surface charging that combines the effects of both spacecraft material properties and severe environments, often called worst-cases. A series of simulations with the SPIS-GEO tool (Spacecraft Plasma Interaction Software) is analysed in order to determine if a worst-case environment can be extracted from the literature. The simulation especially focuses on the conductivity parameters, especially radiation induced. It is found hardly feasible to define a single and global worst-case, applicable to all situations.