Battery pack

A battery pack comprising:

• a cell assembly comprising a plurality of secondary batteries;
• and
• a pack case comprising:
• a bottom part having a plate shape and located under the cell assembly;
• and
• a side wall part provided on the bottom part and protruding vertically from the bottom part to a preset height, the pack case accommodating the cell assembly in an inner space defined by the bottom part and the side wall part,
• wherein the side wall part includes a first side wall and a second side wall,
• wherein the second side wall includes three planar walls and two protrusions facing towards each other,
• wherein the first side wall extends between the two protrusions, and
• wherein the first side wall is hollow in a direction at least partially perpendicular to a thickness direction of the first side wall, and comprises an inwardly open inlet open at the inner space and an outwardly open outlet.