A battery capable of improving the constant output discharge capacity is provided. A battery includes a cathode, an anode, and an electrolyte. The cathode contains iron sulfide. The anode contains lithium metal or a lithium alloy. A ratio of a discharge capacity per unit area of the cathode to a discharge capacity per unit area of the anode (the discharge capacity per unit area of the cathode/the discharge capacity per unit area of the anode) is more than 1 and 1.4 or less.