<p>Renewable energy resources (RERs) are essential components of modern energy grids. However, their inherent intermittency and variability impose significant challenges to grid stability and reliability. As more renewable energy sources are integrated into the power grid, balancing energy supply and demand becomes more difficult. This creates challenges in keeping the grid stable and affects energy planning and electricity management. To address these challenges effectively, innovative approaches are very important. Energy storage systems (ESS) offer a promising solution to these challenges. They adjust excess renewable energy to meet grid demand. The objective of this study is to review the role of battery energy storage systems (BESS) in modern utility grids, emphasizing their applications in enabling the large-scale integration of RERs. The study also reviews key applications of BESS, including peak shaving, load shifting, backup power, grid stabilization, and islanded operation. It provides readers with an understanding of the impact of BESS on renewable energy systems. It highlights the main characteristics of BESS, such as energy and power density, efficiency, cost, safety, and long-term performance. It further identifies key challenges in scaling, reliability, and sustainability. The result of this study also highlights opportunities for improvement, especially in the integration of BESS with IoT-based wireless sensor networks and energy-autonomous sensor nodes.</p>