The purpose of this paper is to propose an energy management strategy (EMS) based on flatness control method for a standalone hybrid photovoltaic-battery system. The goal of the proposed method is to use non-linear flatness theory to develop an efficient EMS in order to provide a stable DC bus voltage and an optimal power sharing process between the solar array and the battery. The suggested EMS is responsible for balancing the power reference for the PV system and the battery while keeping the DC bus voltage steady and performing at its reference value. In order to maximize the PV's power, a perturb and observe with a variable step size (VSSP and P & O) based maximum power point tracking (MPPT) method with a DC/DC boost converter was used. In addition, a DC/DC bidirectional converter was developed to control the charging and discharging process of the battery. Moreover, the proposed EMS strategy was verified in a MATLAB (R)/Simulink-based simulation environment by subjecting it to a variety of scenarios, including those with varying degrees of irradiation and sudden changes in load. The obtained results show that the presented EMS method was able to keep the bus voltage stable despite changes in load or solar radiation. Furthermore, the EMS By minimizing bus voltage spikes, the technique also ensured excellent power quality which helped the battery's operation in terms of lifetime and efficiency. Finally, the suggested strategy has a minimum overshoot rate in the bus voltage and higher tracking efficiency compared with the classical load following (LF) strategy under various load conditions.