A power storage device , comprising: a secondary battery ; and a charging device for charging the secondary battery, wherein the secondary battery is configured to have a positive electrode , a negative electrode , and a nonaqueous electrolyte disposed between the positive and negative electrodes, in the secondary battery, metal ions are movable between the positive and negative electrodes through the nonaqueous electrolyte, and the positive and negative electrodes are charged/discharged when insertion/extraction reactions of the metal ions are carried out through the nonaqueous electrolyte, the positive electrode including a positive-electrode active-material layer capable of inserting/extracting the metal ions, the positive-electrode active-material layer being formed on a surface of a first current collector and having an average thickness of 0.3 mm or greater, a porosity of the positive-electrode active-material layer being 15% to 60%, and the negative electrode including a negative-electrode active-material layer capable of inserting/extracting the metal ions, the negative-electrode active-material layer being formed on a surface of a second current collector and having an average thickness of 0.3 mm or greater, a porosity of the negative-electrode active-material layer being 15% to 60%, the charging device is electrically connected to the secondary battery, and is adapted to charge the secondary battery only at a constant current, and the secondary battery is so configured that when the secondary battery is charged at 1/8 C to its end-of-charge voltage by the charging device, its capacity is set to be 80% to 97% of the design capacity calculated from the inherent capacity per unit weight of the positive and negative electrodes, wherein the power storage device comprises a battery pack configured to have a plurality of the secondary batteries connected in series, wherein the charging device is adapted to charge the secondary batteries pack by pack. a secondary battery ; and a charging device for charging the secondary battery, wherein the secondary battery is configured to have a positive electrode , a negative electrode , and a nonaqueous electrolyte disposed between the positive and negative electrodes, in the secondary battery, metal ions are movable between the positive and negative electrodes through the nonaqueous electrolyte, and the positive and negative electrodes are charged/discharged when insertion/extraction reactions of the metal ions are carried out through the nonaqueous electrolyte, the positive electrode including a positive-electrode active-material layer capable of inserting/extracting the metal ions, the positive-electrode active-material layer being formed on a surface of a first current collector and having an average thickness of 0.3 mm or greater, a porosity of the positive-electrode active-material layer being 15% to 60%, and the negative electrode including a negative-electrode active-material layer capable of inserting/extracting the metal ions, the negative-electrode active-material layer being formed on a surface of a second current collector and having an average thickness of 0.3 mm or greater, a porosity of the negative-electrode active-material layer being 15% to 60%, the charging device is electrically connected to the secondary battery, and is adapted to charge the secondary battery only at a constant current, and the secondary battery is so configured that when the secondary battery is charged at 1/8 C to its end-of-charge voltage by the charging device, its capacity is set to be 80% to 97% of the design capacity calculated from the inherent capacity per unit weight of the positive and negative electrodes, wherein the power storage device comprises a battery pack configured to have a plurality of the secondary batteries connected in series, wherein the charging device is adapted to charge the secondary batteries pack by pack. <EOS>