The present disclosure provides a surgical instrument including a handle assembly and an interchangeable shaft assembly. The shaft assembly includes an elongate shaft, and an end effector extending distally from the elongate shaft. The handle assembly includes a motor configured to effectuate at least one motion in the end effector while said handle assembly is coupled to the shaft assembly. A power assembly is separably couplable to the handle assembly. The power assembly includes a power source configured to power the motor and a power management controller in communication with the power source. The power management controller is configured to receive an input signal corresponding to at least one power requirement of the shaft assembly. The power management controller is configured to modulate power output of the power source to the motor to conform the power output with the at least one power requirement of the shaft assembly.
