Thin battery and battery device

This thin battery includes a sheet-form electrode group and an outer case housing the electrode group, wherein the electrode group contains a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive and negative electrodes, and there is a lubricating substance with a lubricating action interposed between the electrode group and the inner surface of the outer case. The lubricating substance may be for example an inert gas. The inert gas may for example contain at least one of nitrogen and argon. The lubricating substance is ideally at least present between the end surfaces of the electrode group on both sides in the thickness direction and the main flat surfaces of the inner surface of the outer case facing said end surfaces.