Battery drain circuit for surgical instrument

A surgical instrument, comprising:

• (a) a shaft assembly having a distal end portion and a proximal end portion, the distal end portion including an end effector projecting distally, therefrom;
• (b) a handle assembly configured to receive the proximal end portion of the shaft assembly, wherein the handle assembly includes a battery dock;
• and
• (c) a battery unit configured to be received by the battery dock such that the battery unit is in electrical communication with at least one of the shaft assembly or the handle assembly, the battery unit including:
• (i) a casing;
• (ii) an anode contact and a cathode contact positioned within the casing and configured to electrically connect to at least one battery;
• and
• (iii) a discharge drain including:
• (A) a discharge contact configured to selectively move from an open position to a closed position, wherein at least one of the anode contact and the cathode contact is electrically disconnected from the discharge drain in the open position, and wherein each of the anode contact and the cathode contact is electrically connected to the discharge drain in the closed position, and
• (B) a controller configured to sense an initial discharge of the battery unit, wherein the controller includes a timer configured to delay draining any remaining electrical power from the at least one battery connected to the anode contact and the cathode contact until the predetermined amount of time has elapsed after the initial discharge of the battery unit.

A method of discharging a remaining electrical power from at least one battery of a surgical instrument, the surgical instrument including a handle assembly, a shaft assembly extending distally from the handle assembly, an end effector located at a distal end of the shaft assembly, and a battery unit, wherein the battery unit includes at least one battery and a discharge drain, wherein the handle assembly includes a battery dock configured to receive the battery unit such that the battery unit is in electrical communication with at least one of the shaft assembly or the handle assembly, the method comprising:

• (a) discharging an electrical power from the at least one battery to at least one of the handle assembly or the shaft assembly;
• (b) detaching the battery unit from the battery dock;
• (c) sensing the act of detaching the battery unit from the battery dock using a sensor that produces a signal;
• (d) sending the signal from the sensor to a microprocessor indicating that the battery unit has been detached from the battery dock;
• (e) coupling the at least one battery with the discharge drain in response to sensing the act of detaching the battery unit from the battery dock;
• and
• (f) draining a remaining power from the at least one battery via the discharge drain while the battery unit remains detached from the battery dock.