Patent ID: 8742728

Claim:
A rechargeable battery system that controls charge/discharge of a lithium ion rechargeable battery, comprising: an internal resistance detection unit that detects or estimates an internal resistance value indicating an internal resistance at the lithium ion rechargeable battery; a discharge control unit that executes control so as to set a discharge suspension period while the lithium ion rechargeable battery is discharged if the internal resistance value detected via the internal resistance detection unit during discharge of the lithium ion rechargeable battery exceeds a first threshold value; and a battery condition detection unit that detects a battery voltage, a charge/discharge current, a charge/discharge time length and a battery surface temperature at the lithium ion rechargeable battery, wherein: the internal resistance detection unit estimates the internal resistance at the lithium ion rechargeable battery based upon a cumulative charge/discharge electricity quantity calculated based upon the battery voltage, the charge/discharge current, the charge/discharge time length and the battery surface temperature.