A surgical instrument comprises a body, a transmission assembly, and a switch. The body comprises a control unit and an integral power source. The power source is operable to selectively deliver power to the control unit. The transmission assembly extends distally from the body. The transmission assembly also includes an end effector driven by the control unit. The switch is in communication with the control unit and the power source. The transmission assembly is operable to actuate the switch to enable delivery of power from the power source to the control unit.