The Thesis work has been held inside the development program of the EVERGRIN project, a new concept kit aimed to transform an old internal combustion engine vehicle into a full electric vehicle. The main objective of the design process that is described inside the thesis was to design the power box of the retrofit kit. Starting from the vehicle’s hood scansions every aspect of the assembly has been covered according to the requirement requested by the company. So the work started from the design of the structural components, accompanied by some mechanical simulation to prove whether the parameters used are acceptable, to the choice and positioning of all the electrical and electronical components inside and outside the power box to guarantee the requested IP rating.