The distributed energy sources and the energy-storage system are considered a critical solutions for integrating renewable energy sources in Microgrids. The optimal size of battery storage is essential to overcome the intermittency of Renewable energy sources for energy-saving and cost-benefit. The present paper addresses the determination of optimal sizing of the battery energy storage system (BESS) in a dis-patchable and non-dis-patchable energy sources based micro-grid. The main contribution of the paper is: (i) to obtain an optimal size of battery energy storage in a combined heat and power (CHP), Micro-Turbine (MT), Fuel Cell (FC), Wind Turbine (WT) and Solar Photovoltaic (PV) based hybrid system (ii) to determine the impact of renewable and Distributed Generation (DGs) on the sizing of BESS (iii) Optimal scheduling of dispatchable units (iv) The dispatchable schedule of CHP, MT and FC with ramp rate control. The hourly spinning reserve, minimum up, and down-time constraints have been taken into account. In addition, a linear piecewise cost function is considered for the cost-benefit analysis. The minimum daily energy loss profile, voltage, and power loss have been obtained. The state of charge (SOC) of battery profile, the cost of battery energy per day, unit commitment (UC) cost, startup, and shunt down cost have also been determined. The proposed technique has been tested on the IEEE-33 bus test system considering realistic ZIP load. The general algebraic modelling system (GAMS) was used to solve an optimization problem. The increment in total benefit obtained is 11.44% with using battery energy storage. The annual cost of energy loss saving of $62448.51 (61.99%) has been obtained, and the increment in minimum voltage obtained is 2.831% with the proposed technique for the 33 bus test system.