Abstract: A control unit for a battery-operated device is proposed which via an existing control connection recognizes an overload of the battery and/or of the electric device. The control connection of a temperature-dependent resistor is used, which is thermally connected to the rechargeable battery. This connection, which is typically usable to control a charging unit, now serves during the battery operation of the electric device as a control output for monitoring the battery temperature. Since the temperature gradient is also detected, this signal can also be used to monitor the overload of the electric device, which for instance is an electric motor.