BATTERY PACK

A battery pack () includes: an outer case (); one or more battery cells (-); and a cell case (), which is housed in the outer case () and houses the battery cell(s) (-). The outer case () has: an upper surface (wall) (), in which a terminal-opening part () for exposing a terminal () is provided; a bottom wall (); and a plurality of side surfaces (walls) (-) extending upward from the bottom wall (). The battery cell(s) (-) is (are) disposed parallel to the bottom wall (). An opening (-) is provided in a specific side surface (), from among the plurality of side surfaces (-), that faces an end surface of the battery cell(s) (-) in a longitudinal direction.