Abstract: A secondary battery including an electrode assembly including a positive electrode plate having a positive electrode uncoated portion, a negative electrode plate having a negative electrode uncoated portion, and a separator between the positive electrode plate and the negative electrode plate, a case including a side plate with a cylindrical body, the case accommodating the electrode assembly and a lower plate, the lower plate sealing a lower portion of the side plate, and a cap assembly coupled to an upper portion of the case and electrically connected to the positive electrode plate, the negative electrode uncoated portion including a negative electrode extension uncoated portion of which one end portion is folded, extends downward from the electrode assembly, and is connected to the lower plate of the case.