Patent ID: 8901890

Claim:
A battery system comprising: a plurality of battery units, the battery unit having a battery bank made up by connecting a plurality of storage batteries with each other, and a switching circuit, connected in series to the battery bank, the plural battery units being connected in parallel with each other, wherein the switching circuit is made up by connecting a first circuit comprising a first switch connected in series to a precharge resistor in parallel with a second circuit comprising a second switch, wherein the plural battery units each comprise: a battery bank voltage detector that detects a voltage difference between the respective ends of the battery bank; and a first current detector that detects a current flowing through the battery bank, wherein the battery system has a second current detector that detects a current flowing through the battery system, and is provided with a controller that controls respective outputs of the plural battery units, and wherein the controller turns the first switch into the on state in a connection-target battery unit to serve as a target for connection when the connection-target battery unit is connected to the battery system, turning the first switch into the off state after the second switch is turned into the off state, whereupon the on/off state of the first switch and the second switch, respectively, is controlled on the basis of a current detection information piece of the first current detector, a current detection information piece of the second current detector, and a voltage detection information piece of the battery bank voltage detector when the second switch is turned into the off state.