The research aimed to evaluate the BESS system for primary frequency regulation at the Marañón hydroelectric plant. The research approach is quantitative, the method is deductive - descriptive, the type of research that was carried out is applied to a level of descriptive - correlational research and the design was non - experimental with longitudinal cut, frequency data of the system was used compared with the frequency of the speed regulator of the Marañón hydroelectric plant, according to the data obtained another comparison was made with the system frequency and the plant frequency after the installation of the BESS system, finally a simulation of the data obtained is carried out to see the behavior of the batteries during the power contribution time for primary frequency regulation. Concluding that, facing disturbances in the Peruvian power system, the BESS system is a good alte...