A motor driven actuator device includes an actuator motor; a controller; an input for receiving an external power supply; and a battery pack electrically connected to selectively drive the actuator motor, and electrically connectable to the external power supply for charging. During charging of the battery pack, the controller is configured to compare a measured charge level with a pre-determined charge level required to complete at least two battery shutdown events under battery power alone. During subsequent actuator device operation, the controller is configured to: determine if the external power supply is invalid, instruct a battery shutdown event causing the battery to be discharged, with enough charge in the battery to complete at least one further battery shutdown event; and, subsequently detect when the external power supply becomes valid, and resume actuator device operation under the external power supply, while simultaneously recharging the battery pack to at least the pre-determined charge level.