A method for testing capacity of at least one energy storage device of a pitch drive mechanism to drive a first rotor blade of a wind turbine , the wind turbine connected to a power grid , the method comprising: defining a rotor position range for implementing a first test procedure for the at least one energy storage device , wherein the rotor position range comprises rotor positions in which a motor torque of a pitch drive motor of the pitch drive mechanism acts against a predetermined threshold of gravity during pitching of the first rotor blade toward a feathered pitch angle, and wherein defining the rotor position range further comprises selecting rotor positions that require an amount of energy equal to or above the predetermined threshold of gravity to pitch the first rotor blade towards the feathered pitch angle and excluding rotor positions that require an amount of energy below the predetermined threshold of gravity to pitch the first rotor blade towards the feathered pitch angle; monitoring a rotor position of the first rotor blade ; when the rotor position of the first rotor blade enters the rotor position range, initiating the first test procedure, the first test procedure comprising: pitching the first rotor blade toward the feathered pitch angle via the at least one energy storage device ; measuring at least one operating condition of the at least one energy storage device during pitching; and, determining a capacity of the at least one energy storage device to drive the first rotor blade based on the at least one operating condition of the at least one energy storage device . defining a rotor position range for implementing a first test procedure for the at least one energy storage device , wherein the rotor position range comprises rotor positions in which a motor torque of a pitch drive motor of the pitch drive mechanism acts against a predetermined threshold of gravity during pitching of the first rotor blade toward a feathered pitch angle, and wherein defining the rotor position range further comprises selecting rotor positions that require an amount of energy equal to or above the predetermined threshold of gravity to pitch the first rotor blade towards the feathered pitch angle and excluding rotor positions that require an amount of energy below the predetermined threshold of gravity to pitch the first rotor blade towards the feathered pitch angle; monitoring a rotor position of the first rotor blade ; when the rotor position of the first rotor blade enters the rotor position range, initiating the first test procedure, the first test procedure comprising: pitching the first rotor blade toward the feathered pitch angle via the at least one energy storage device ; measuring at least one operating condition of the at least one energy storage device during pitching; and, determining a capacity of the at least one energy storage device to drive the first rotor blade based on the at least one operating condition of the at least one energy storage device . pitching the first rotor blade toward the feathered pitch angle via the at least one energy storage device ; measuring at least one operating condition of the at least one energy storage device during pitching; and, determining a capacity of the at least one energy storage device to drive the first rotor blade based on the at least one operating condition of the at least one energy storage device . <EOS>