Following the rise in demand for clean energy production in order to reduce CO2 emissions, power systems are facing challenges caused by the growing use of non-programmable renewable energy sources (RESs). In this regard, storage systems can play a role of primary importance since they are supposed to provide ancillary services. These are necessary for supporting RESs and thus keeping the grid stable. The present paper illustrates a methodology to guide a potential investor with the choice of a battery energy storage system (BESS) for the provision of grid-supporting services, considering both grid necessities and profitability. In particular, the methodology proposes a model that simulates the battery behaviour and the provision of the services including also an economic analysis to evaluate the profitability of the investment.