Secondary battery and assembled battery

An assembled battery (10) according to the present invention is constructed by connecting a plurality of chargeable and dischargeable cells (12) in series, this assembled battery (10) including a plurality of cells (12), each cell (12) including a flat-shaped electrode body (80) which has a positive electrode and a negative electrode and a container (14) which houses the electrode body (80) and an electrolyte, wherein the plurality of cells (12) are constrained in a state where the cells (12) are aligned so that flat surfaces of the electrode bodies (80) oppose each other and a load is applied to the cells (12) in an array direction, and a spring constant of the electrode body (80) in the array direction in each of the constrained cells (12) is 10,000 kgf/mm or less.