There is provided a battery system including parallel-connected bus bars each connecting the plurality of prismatic battery cells in parallel, and a safety mechanism configured to be capable of interrupting a current path of prismatic battery cells connected in parallel by the parallel-connected bus bars, where the sealing plate of one of the prismatic battery cells convexly deforms due to a rise in an internal pressure of this prismatic battery cell when an abnormality occurs, the sealing plate that has convexly deformed comes into contact with the parallel-connected bus bars to form external short circuitry between the electrode terminals that are positive and negative of one prismatic battery cell connected in parallel to the prismatic battery cell with the abnormality, and external short circuitry activates the safety mechanism that interrupts a current flowing into the prismatic battery cell with the abnormality.