Abstract: The method comprises: using a plurality of storage devices, of the same or different types of storage technologies, with the same or different power supply capacities; measuring voltage, current and temperature values, in each of the storage devices; acquiring these measured values and processing them to carry out: a first calculation of a degradation state of each of the storage devices; and a second calculation of a state of function (SoF) of the electrical energy storage unit to provide an electrical service according to a result obtained in the first calculation and the conditions or needs of the power grid; and determining whether or not a power profile for performing the electrical service may be provided, taking into consideration the calculated SoF.