A power supply unit includes: (A) a housing having a shape like a polygonal column; (B) a secondary battery cell contained in the housing; (C) charge/discharge control means contained in the housing and connected to the secondary battery cell; (D) at least one power input section disposed on the housing and connected to the charge/discharge control means; and (E) at least one power output section disposed on the housing and connected to the charge/discharge control means.
