BATTERY PACK

Discussed is a pack case including a module area where a cell stack is placed, wherein the pack case includes a base plate that supports a lower portion of the cell stack, a main partition wall extending across the base plate and perpendicularly coupled to a central portion of the base plate, a side wall perpendicularly coupled to an edge of the base plate along a perimeter of the base plate, and an auxiliary partition wall of which opposite ends are coupled to the main partition wall and the side wall, respectively, and which includes a pair of reinforcement plates coupled to each other, and a reinforcement plate of the pair of reinforcement plates includes a plurality of reinforcement ribs protruding and extending in a longitudinal direction of the reinforcement plate.