A wind turbine with pitch motors for pitching rotor blades, further comprises a first sensor unit and a second sensor unit configured to measure at least one of a voltage value and a current value at a first location and a second location, wherein the voltage value and current value are indicative of the condition of a backup power supply. When the second location is different from the first location the measurement results are independent from each other. A comparison of the two measurements then gives a level of confidence how these measurements match each other. In case of a low level of confidence the pitch drive motors are caused to pitch the rotor blades into a feathering position.