This paper estimates the profit of the joint operation of a wind farm and a li-ion battery energy storage system (BESS) in the Iberian electricity market (MIBEL). The day-ahead and first intraday energy markets, and the tertiary regulation market are considered to optimize the joint operation of both assets. A rolling window combined with a non-linear optimization model are used to design the operation strategy. The BESS lifetime (as a function of the depth of discharge) is considered in the optimization problem, and different BESS capacities and initial state of charge values are tested to determine their approximate optimum values. The model and strategy designed were tested using real data from the MIBEL market and predicted data from Sotavento wind farm. The resulting incomes were compared to the BESS investments costs to determine, for a given capacity, when the project becomes viable.