An electrical appliance, such as a power tool, has an electrical motor, a control circuit connected to the motor, and a rechargeable LI-ion battery pack for powering the motor via the control circuit. A battery protection circuit has a detection circuit for detecting an adverse operating condition of the battery pack and then providing a disabling signal indicative of that condition. Also included is an interface circuit provided between the battery circuit and the control circuit for sending said disabling signal to the control circuit to switch off the motor.