BATTERY PACK

Thermal runaway of a battery cell is prevented from being induced in another battery cell and catching fire of the battery cell is prevented, ensuring safety. A battery pack includes a battery assembly including battery cells (1) parallel to one another and an outer case (4) housing the battery assembly. Each battery cell includes a discharge valve provided on an end surface thereof, and an end-surface electrode (1a, 1b) provided at an end portion thereof and arranged on the same plane. A welding surface (3B) of the lead plate (3) is connected to the end-surface electrode (1a, 1b) arranged on the same plane. The battery pack includes a backflow-restricting layer (5) disposed on a non-welding surface (3A) of the lead plate (3) in the outer case (4). The lead plate (3) has a gas permeation gap (33) therein allowing an exhaust gas discharged from the discharge valve to pass in a discharge direction of the backflow-restricting layer (5) from the battery cell (1). The backflow-restricting layer (5) includes a resistance part (7) configured to allow the exhaust gas passing through gas permeation gap (33) to pass in the discharge direction, and to suppress or prevent the exhaust gas from passing in a direction opposite to the discharge direction.