The invention concerns a method comprising two fundamental steps. The first one is an innovative process of characterization of the energetic efficiency performed during a charging process of an accumulator, whereby one derives a series of information concerning: the dependency of the electric parameters of the accumulator on the state of charge; the dependency of the efficiency of the charging system on the voltage and current at the output of the charging system. The second step of the proposed method is a process of data calculation for the prediction of the energetic efficiency, wherein one simulates one or more charging processes. The method can be realized by means of a charging system able to perform both a standard process for charging the accumulator and a process of characterization of the energetic efficiency, and a process of prediction of the energetic efficiency.