A secondary battery configured to effectively estimate the life or degradation of the secondary battery as the secondary battery degrades includes a packaging material, an electrode assembly, a first electrode lead, a second electrode lead, a first measuring lead, and a second measuring lead. The electrode assembly includes a stack having a plurality of first electrode plates at respective first locations within the stack and a plurality of second electrode plates at respective second locations within the stack, the first and second locations alternating with one another and having a separator interposed between each of the first and second locations. The electrode assembly further includes a first measuring plate and a second measuring plate having the same polarity as the first electrode plates and located at at least one of the first locations within the stack.