An electric power tool is powered by a plurality of battery packs connected in series. The electric power tool comprises a controller configured to receive signals outputted from the integrated circuits located in each of the battery packs. A first voltage level-shifter is disposed between the controller of the electric power tool and one of the integrated circuits of the battery packs. The first voltage level-shifter is configured to shift the voltage level of the signal outputted from the respective integrated circuit to the tool controller to an acceptable level for the controller.