Battery energy storage is the use of rechargeable batteries to store excess electricity generated by renewable energy sources such as solar panels or wind turbines. Battery energy storage systems typically consist of batteries, battery management systems, inverters and monitoring systems and can be installed in residential, commercial or utility-scale applications. Commonly used rechargeable battery technologies in battery energy storage systems include lithium-ion batteries, lead-acid batteries, flow batteries, and sodium-ion batteries. Battery energy storage can help reduce dependence on fossil fuels and promote the adoption of renewable energy. It can also help improve power quality and reliability by providing backup power during outages or periods of high demand. For utility-scale applications, battery storage can help grid operators manage peak demand, reduce the need for new power plants and transmission lines, and integrate renewable energy into the grid. In conclusion, battery energy storage is a key technology to improve the reliability and resilience of energy systems, promote sustainability, and transform the energy landscape into a low-carbon future.