A traction battery charging station for charging a traction battery of a motor vehicle having an electric traction motor. The charging station includes a converter that feeds DC voltage into a pair of two charging lines during charging operation, a charging controller, and an insulation monitor having two measuring resistors that are each connected to a charging line and are able to be connected to protective earth via a respective resistor switch. The insulation monitor monitors the electrical insulation of the pair of charging lines with respect to protective earth during non-charging and during charging of the traction battery. A test mode controller has a non-restricted non-charging test mode in which one resistor switch is closed and the other resistor switch is open at the same time, and a symmetric charging test mode in which both resistor switches are closed at the same time or open at the same time.