A lithium-ion secondary battery system is provided which can improve the cycle life and the storage property of a lithium-ion secondary battery and can decrease a discharge capacity which cannot be recharged. The lithium-ion secondary battery system includes a lithium-ion secondary battery having a cathode, an anode including carbon, and a non-aqueous electrolyte; a charge/discharge circuit for putting the lithium-ion secondary battery on charge according to a charge control parameter; and an arithmetic processing section for controlling the charge/discharge circuit. The arithmetic processing section obtains battery characteristics of the lithium-ion secondary battery, changes a value of the charge control parameter when the arithmetic processing section determines that the battery characteristics satisfies a condition for changing the charge control parameter, and restores the value of the charge control parameter to the value before the change when the charge for the lithium-ion secondary battery is finished.