A battery system includes a battery unit in which battery arms are connected in parallel, and a charge/discharge control device that controls charge/discharge of the battery unit. Each of the battery arms includes: a battery composed of one or more battery cells connected in series; a switch connected in series to the battery; and a battery monitoring device that, in a case of having detected abnormality of the battery, opens the switch to thereby isolate the battery arm including the abnormal battery, and sends a switch opening signal indicating that the switch has been opened to the charge/discharge control device. The charge/discharge control device performs a control to reduce a charge/discharge current or charge/discharge power of the battery unit when the switch opening signal is sent from the battery monitoring device of the battery unit to the charge/discharge control device.