The battery system according to an embodiment of the present invention is provided with a first cell and a second cell connected in parallel to the first cell. The first cell includes a lead storage cell. The second cell includes a non-aqueous electrolytic cell. The non-aqueous electrolytic cell is provided with a positive electrode and a negative electrode. The negative electrode includes a negative-electrode mixture layer, and the negative-electrode mixture layer includes lithium titanate. The negative-electrode mixture layer has a coating weight in the range of 15 g/m2-100 g/m2 and a thickness in the range of 5 µm-50 µm. The positive electrode includes a positive-electrode active material (LiMn2-xM(a)xO4). The ratio of the cell capacity of the second cell to the cell capacity of the first cell is in the range of 1/133-1/2.
