A case (20) of each battery cell (1) houses a current interrupt device (30) that cuts-off current when internal pressure exceeds a set pressure. The case has a rectangular outline with a pair of opposing planar surfaces (20A). An electrode unit (10), which is a stack of positive and negative electrode plates (10A) with intervening separators (10C), and the current interrupt device are disposed between the pair of opposing planar surfaces. A plurality of battery cells is stacked with opposing planar surfaces opposite each other to form a battery block (2). The power source apparatus has a pair of endplates (4) disposed at the ends of the battery block, the pair of endplates is connected by connecting components (5), and the pair of endplates holds the battery cells in the stacked configuration applying pressure in a direction perpendicular to the opposing planar surfaces.