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