A surgical instrument comprising: an end effector comprising a moveable cutting instrument; a shaft connected at its distal end to the end effector; and a handle connected to a proximate end of the shaft, wherein the handle comprises: an electric motor for actuating the cutting instrument; a removable battery pack for powering the motor, wherein the battery pack comprises a plurality of battery cells, wherein the plurality of battery cells comprises a first plurality of battery cells that are connected in series in the removable battery pack and a second plurality of battery cells that are connected in series in the removable battery pack; and a battery cell connector, separate from the battery pack, that connects in series the first plurality of series-connected battery cells to the second plurality of series-connected battery cells when the battery pack is installed in the instrument, wherein the first plurality of series-connected battery cells is not connected with the second plurality of series-connected battery cells in the removable battery pack until connected in series by the battery cell connector upon installation of the battery pack in the instrument. an end effector comprising a moveable cutting instrument; a shaft connected at its distal end to the end effector; and a handle connected to a proximate end of the shaft, wherein the handle comprises: an electric motor for actuating the cutting instrument; a removable battery pack for powering the motor, wherein the battery pack comprises a plurality of battery cells, wherein the plurality of battery cells comprises a first plurality of battery cells that are connected in series in the removable battery pack and a second plurality of battery cells that are connected in series in the removable battery pack; and a battery cell connector, separate from the battery pack, that connects in series the first plurality of series-connected battery cells to the second plurality of series-connected battery cells when the battery pack is installed in the instrument, wherein the first plurality of series-connected battery cells is not connected with the second plurality of series-connected battery cells in the removable battery pack until connected in series by the battery cell connector upon installation of the battery pack in the instrument. an electric motor for actuating the cutting instrument; a removable battery pack for powering the motor, wherein the battery pack comprises a plurality of battery cells, wherein the plurality of battery cells comprises a first plurality of battery cells that are connected in series in the removable battery pack and a second plurality of battery cells that are connected in series in the removable battery pack; and a battery cell connector, separate from the battery pack, that connects in series the first plurality of series-connected battery cells to the second plurality of series-connected battery cells when the battery pack is installed in the instrument, wherein the first plurality of series-connected battery cells is not connected with the second plurality of series-connected battery cells in the removable battery pack until connected in series by the battery cell connector upon installation of the battery pack in the instrument.