A battery system comprising: a battery module; a cooling channel disposed adjacent to the battery module; a ground wire configured to electrically connect the cooling channel and a vehicle body; characterized in that the battery system further comprises a leakage current blocking device configured to interrupt an electrical connection of the cooling channel and the vehicle body when a leakage current occurs in the battery module, the leakage current blocking device being disposed outside the battery module and having a first acicular structure and a second acicular structure, which are electrically connected to two points inside the battery module, respectively, wherein the leakage current blocking device is configured such that a leakage current between the two points inside the battery module causes an electric spark to occur between the first and second acicular structures, and wherein the leakage current blocking device further comprises: a spark induction chamber having an inner space, in which the first and second acicular structures are arranged, and having a piston which is configured to move as a gas in the inner space expands due to the occurrence of an electric spark between the first and second acicular structures; a switch configured to be operated by the piston; and a relay configured to determine an electrical connection state of the ground wire according to the operation of the switch. a battery module; a cooling channel disposed adjacent to the battery module; a ground wire configured to electrically connect the cooling channel and a vehicle body; characterized in that the battery system further comprises a leakage current blocking device configured to interrupt an electrical connection of the cooling channel and the vehicle body when a leakage current occurs in the battery module, the leakage current blocking device being disposed outside the battery module and having a first acicular structure and a second acicular structure, which are electrically connected to two points inside the battery module, respectively, wherein the leakage current blocking device is configured such that a leakage current between the two points inside the battery module causes an electric spark to occur between the first and second acicular structures, and wherein the leakage current blocking device further comprises: a spark induction chamber having an inner space, in which the first and second acicular structures are arranged, and having a piston which is configured to move as a gas in the inner space expands due to the occurrence of an electric spark between the first and second acicular structures; a switch configured to be operated by the piston; and a relay configured to determine an electrical connection state of the ground wire according to the operation of the switch. a spark induction chamber having an inner space, in which the first and second acicular structures are arranged, and having a piston which is configured to move as a gas in the inner space expands due to the occurrence of an electric spark between the first and second acicular structures; a switch configured to be operated by the piston; and a relay configured to determine an electrical connection state of the ground wire according to the operation of the switch.