Battery Energy Storage Systems (BESS) are advanced energy solutions designed to store electrical energy for later use, playing a critical role in modern power systems and renewable energy integration. This course provides a comprehensive understanding of BESS technologies, components, design principles, operation, and applications across residential, commercial, industrial, and utility-scale sectors. Participants will learn about different battery chemistries including lithium-ion, lithium iron phosphate (LFP), lead-acid, sodium-ion, and flow batteries, along with their performance characteristics, advantages, limitations, and safety considerations. The course covers key system components such as battery packs, Battery Management Systems (BMS), Power Conversion Systems (PCS), inverters, Energy Management Systems (EMS), thermal management systems, fire protection systems, and SCADA integration. Learners will gain knowledge of energy storage sizing, load analysis, charging and discharging strategies, peak shaving, load shifting, frequency regulation, renewable energy integration, backup power applications, and grid stabilization techniques. In addition, the program explores system architecture, electrical protection, safety standards, installation practices, operation and maintenance procedures, lifecycle analysis, and performance optimization of BESS projects. Practical insights into solar-plus-storage systems, microgrids, EV charging integration, utility-scale deployments, and emerging trends in smart grids and sustainable energy infrastructure are also included. The course is designed to equip students, engineers, technicians, and energy professionals with the technical skills and industry knowledge required to design, operate, maintain, and manage modern battery energy storage solutions in alignment with global energy transition goals and evolving power sector demands.