Patent ID: 8531154

Claim:
A battery system including a secondary battery and using electric energy of this secondary battery for a power source, the battery system comprising: an upper-limit electrical quantity setting means for setting an upper-limit electrical quantity which is an upper limit of an electrical quantity obtainable from the secondary battery to a lower quantity than a full-charge electrical quantity which is an electrical quantity obtainable from the secondary battery in a full charge state, the upper-limit electrical quantity setting means being arranged to set the upper-limit electrical quantity to a value having a difference from the full-charge electrical quantity so that the difference is smaller as deterioration of the secondary battery progresses, and so that the upper-limit electrical quantity is gradually decreased as compared with a decrease in the full-charge electrical quantity caused by the deterioration of the secondary battery; and a charging means for charging the secondary battery under the condition that the upper-limit electrical quantity is an upper limit when the secondary battery is charged.