We consider in this paper a wireless network powered by a smart grid. The base stations are endowed with backup battery in order to prevent possible power failures in the grid. The battery can also be used for arbitrage purposes wherein the operator can purchase electricity from the grid with a certain price and store it in order to use it later when prices go up. Our aim is to design, on a daily basis, an optimal energy storage strategy, taking into account the electricity price fluctuations in order to reduce the operator's daily energy acquisition cost while satisfying the users traffic requirements and a maximal number of cycles to be performed per day in order to extend the battery lifetime. We do so using a Markov Decision Process (MDP) formulation. With respect to the battery type (Lithium, Lead-acid), cycle and calendar life, we set, on a long-term basis, an optimal battery cycling strategy using a simple exhaustive search algorithm. The aim of this long-term policy is to optimize the operator's return on investment taking into account the battery performance degradation, the increase of user traffic and the seasonality of the electricity prices.