Diesel and gas piston power units are used as a source of electrical power in autonomous power supply systems. For diesel power plants located in remote areas, the main component of the costs are the cost of imported fuel. For gas piston power plants operating on associated gas, the main problem is to ensure the stabilization of the frequency of alternating current with sudden load changes. The use of electrochemical electricity storage devices as part of power plants largely solves these problems. The article considers the choice of storage capacity for fuel economy, reduction the installed capacity of a power plant and frequency stabilization in the power supply system. It is shown that for diesel power plants, the use of electrochemical accumulators leads to both fuel savings and a decrease in its nominal capacity. For gas piston units, where the specific increase in fuel decreases with increasing load, the use of electrochemical accumulators reduces the installed power, but increases fuel consumption. The accumulator parameters for gas piston units are determined by the allowable overload/discharge of the load, and according to the energy intensity, they are determined by the duration of the maximum load, which is smoothed by the drive operation. We present numerical examples for estimating fuel consumption taking into account the efficiency in the charge-discharge processes of storage batteries. The simulation models show the impact of the electrochemical storage device on the stabilization of the frequency of an autonomous electric power supply system.