Abstract: A battery pack adapted to be removably inserted into a battery receiving compartment of a portable electronic device for supplying power to the device is disclosed. The battery pack includes a plurality of cylindrically shaped battery cells and an elongated casing having two spaced apart ends and defining an interior region in which the plurality of battery cells are disposed. Outer cylindrical surfaces of first and second cells and an inner surface of the casing define two elongated open regions extending away from the first end of the casing. The battery pack also includes an integrated circuit board disposed intermediate a first end of the casing and negative and positive connector plates of the cells and includes conductive traces electrically coupled to the connector plates of the first and second cells.