The battery system is provided with a battery 1 that can be recharged, a fuse 8 connected to the battery 1 that blows with excessive current flow, relays 2 connected to the output-side of the battery 1, and a current cut-off circuit 4 that detects excessive battery 1 current and controls the relays 2. The current cut-off circuit 4 detects excessive battery 1 current, and is provided with a timer section 24 that designates a time delay until the relays 2 are switched from ON to OFF. For the delay time of the timer section 24, the fusing current of the fuse 8 is set lower than the maximum cut-off current of the relays 2 and higher than the maximum allowable battery 1 charging and discharging current. In a situation where excessive current greater than the maximum cut-off current of the relays 2 flows through the battery 1, the fuse 8 is blown during the timer 24 delay time, and the current cut-off circuit 4 switches the relays 2 from ON to OFF when the delay time has elapsed.