NOVELTY - A battery pack comprises battery blocks (210) each of which includes base batteries (211) having a cylindrical exterior container, and a battery spacer (212) for holding the base batteries (211) in parallel to each other; and an exterior case (230) that accommodates the battery blocks (210) and the circuit board.    USE - The battery pack can be suitably applied to a power supply for electric devices used outdoors and in particular for power assisted electric bicycles. The battery pack can be suitably applied to a power supply or the like for power assisted electric bicycles.    ADVANTAGE - The battery pack includes a case that has a cylindrical exterior shape and accommodates a circuit board but capable of reducing its exterior size. The battery pack is small and simple, and can be easily assembled but has reliability. The battery pack is capable of changing its output voltage by changing the number of serially-connected battery blocks, and of changing its width by changing the number of parallel units that compose the battery blocks, where providing an optimum exterior shape for applications. The battery pack includes parallel units that are serially connected to each other by bent lead plates so that battery blocks adjacent to each other are coupled to each other can be efficiently and inexpensively assembled. The battery pack can be simply constructed but can reliably prevent that rain water enters through a charging connector. The battery pack can be simply constructed but can reliably prevent problems such as a short circuit caused by rain water even if a discharging connector is immersed in the rain water.    DETAILED DESCRIPTION - A battery pack comprises battery blocks (210) each of which includes base batteries (211) having a cylindrical exterior container, and a battery spacer (212) for holding the base batteries (211) in parallel to each other; pairs of lead plates each of which connect the end surfaces of the base batteries (211) held by the battery spacer (212) in corresponding one of the battery blocks (210) so that the base batteries (211) are connected to each other in parallel, and one of one pair of the lead plates in one battery block (210) is serially connected to one of one pair of the lead plates in another battery block (210) adjacent to the one battery block (210); a circuit board that is electrically connected to the pairs of lead plates; and an exterior case (230) that accommodates the battery blocks (210) and the circuit board. The battery blocks (210) are classified into battery block rows. The classified battery blocks (210) are arranged side by side in parallel to each other so that the end surfaces of the base batteries (211) included in the battery blocks (210) are arranged coplanar with each other. The battery block rows are arranged side by side so that the end surfaces of the base batteries (211) of the battery block rows are opposed to each other and so that the base batteries (211) of the battery block rows are aligned in substantially straight lines and extend in the center axes of cylindrical shapes where composing a battery assembly, where battery block rows that are arranged side by side adjacent to each other include lead plate extension parts that extend along the side surfaces of the battery assembly, and the battery pack comprises lead connection portions (225) that electrically connect the lead plate extension parts to each other. The lead connection portions (225) are alternately arranged on parts of the side surfaces of the battery assembly between adjacent battery block rows to connect the lead plates to each other.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded perspective view of the battery block row of the battery assembly.    Battery block (210)    Base battery (211)    Battery spacer (212)    Spacer coupling portion (216)    Lead connection portion (225)