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As technology advances and cities become more innovative, the need to harvest energy to power intelligent devices at remote locations, such as wireless sensors, is increasing. This paper focuses on studying and simulating an energy management system (EMS) for energy harvesting with a battery and a supercapacitor for low power applications. Lithium-ion batteries are the primary energy storage source for low power applications due to their high energy density and efficiency. On the other hand, the supercapacitors excel in fast charge and discharge. Furthermore, supercapacitors tolerate high currents due to their low equivalent series resistance (ESR). The supercapacitor in the system increases the time response of the power delivery to the load, and it also absorbs the high currents in the system. Moreover, the supercapacitor covers short-time load demand due to the fluctuation of the renewable source. The EMS monitors the proposed system to maintain power to the load either from the renewable source or the energy storage. The power flow of the energy storage is controlled via DC-DC bidirectional converters. The lithium-ion battery is charged via a constant current (CC) using a sliding mode controller (SMC) and a constant voltage (CV) via a typical PI controller. The response of the SMC current controller is compared with PI and Fuzzy current controller. Furthermore, the performance of a system having and not having a supercapacitor is compared. Finally, MATLAB modeling system simulation and experimental implementation results are analyzed and presented.