A battery, suitable for forming a battery pack, includes an electrode assembly having a positive electrode plate and a negative electrode plate, and a separator wound or laminated together, core materials of the negative and positive electrode plates being bared respectively at either end. A bottomed cylindrical outer case having a bottom is connected to either end face of the electrode assembly to serve as a battery terminal. Electrolyte is impregnated in the electrode assembly and a lid connected to the other end face of the electrode assembly and fixedly attached to the outer case with a sealer and an insulator interposed therebetween. A connecting part is a part of the lid so that the connecting part engages with and connects to a bottom part of the outer case of another battery.