To optimize the modes of operation of the power system, improve the power supply reliability to consumers and improve the quality of power supplied to the grid, power storage systems are used as the main and backup power sources. The analysis of the practical experience of using the accumulation system is rather topical nowadays. The authors analyze the practical application in the 0.4 kV power grid “Orelenergo” of an electric energy storage system in the form of a 20 kWh storage device of the MRSK2.0/ESS-50.40 type, installed to improve the quality of electric energy. The article gives an overview of the operating modes of the system’s storage energy and provides the results of an analysis of its control algorithms. It is established that a power grid with unbalanced load application of the considered storage system has worsened operating parameters. This problem arises due to the following design shortcomings: no dependence of the charging/discharging intervals of the drive on the load schedule of consumers, no phase-by-phase control of power output and charging, no shutdown algorithms in an emergency in the power grid. The article concludes with the statement about the incorrect selection of the accumulator intended for correcting power quality indicators. The authors provide recommendations to improve the energy storage systems designed to enhance the quality of electricity to avoid the identified shortcomings.