Batteries are classically used as backup in case of power outages in telecommunications networks to keep the services always active. Recently, network operators use the batteries as a demand response lever, so as to reduce the energy costs and to generate revenues in the energy market. In this work, we study how the telecommunications operator can optimize the use of a battery over a given horizon to reduce energy costs and to perform load curtailments efficiently, as long as the safety usage rules are respected. First, we formulate the related optimization problem as a mixed integer program taking into account the telecommunication engineering and battery operation constraints, as well as the market rules. Second, we give two practical variants of the problem that can be solved to optimality in polynomial time thanks to a graph-oriented algorithm we propose. We also use this algorithm as a heuristic to solve efficiently the main problem. Finally, simulations based on real data from the French telecommunications operator Orange show the relevance of the model and of the graph-oriented algorithm: these prove to be computationally efficient in solving large scale instances, and significant savings and revenues can be generated through our optimized battery management policies.