The Cernay-lès-Reims battery storage facility in the Marne region of France has officially opened, marking a significant milestone as the largest operational battery storage installation in the country. With a power capacity of 240 MW and an energy capacity of 480 MWh, the site was commissioned on October 1st and is developed by TagEnergy, a Portuguese energy company established in 2019. The project received support from the Banque des Territoires, which holds a 49% stake in the facility. This partnership reflects a broader trend of investment in renewable energy infrastructure across Europe. The facility is equipped with 140 Tesla Megapacks, spread over more than three hectares, and is connected to the RTE electricity transmission network at a voltage of 225,000 volts. It provides essential services such as frequency and voltage regulation, which are critical for maintaining stable electricity supply. These functions require rigorous simulations, tests, and certifications to ensure compliance with national and international standards. The project involved several companies, including Eiffage for civil and electrical engineering, and Tewa Solar, which played a key role in project management from the development phase through to commissioning. TagEnergy has built a diverse portfolio of energy projects, including more than 10 GW of solar, wind, and battery storage capacities across several countries. Currently, over 2 GW of these projects are in operation. According to the company, the Cernay-lès-Reims site has already re-injected 70.5 GWh of energy into the grid in four months and completed 145 full charge and discharge cycles in 125 days, demonstrating its efficiency and reliability. The Cernay-lès-Reims battery energy storage system (BESS) was financed by a consortium of financial institutions, including ABN AMRO, NORD/LB, and the Caisse d'Épargne CEPAC. The Banque des Territoires invested in the project in 2025, allowing TagEnergy to maintain majority ownership. This investment is part of a three-year partnership aimed at funding several large battery projects in France. The Banque des Territoires has been active in the electricity storage sector since 2021, with over 250 MW of batteries already in operation and several hundred MW under development.