This research sought to evaluate the technical and economic feasibility of implementing a Battery Energy Storage System to serve as backup for a hydroelectric generator in the face of primary and secondary frequency regulation obligations, considering the changes that could be implemented within the new Complementary Services market. For its development, a historical analysis of the last 10 years (period between 2011 and 2021) of the reservoir levels of the Betania hydroelectric plant was taken into account, which allowed the sizing of the storage systems and the solar photovoltaic array used to meet the requirements as defined in the Primary Frequency Regulation. With this, the value associated to the BESS load was estimated and the budget. However, it was evaluated different sources such as generation, and with this, the most viable alternative was selected and the benefits that this would bring to the hydroelectric power plant.