The invention relates to an energy storage device comprising an arrangement of battery cells (70, 80, 90) in an installation housing (2), wherein groups (I, II, III) of battery cells (70, 80, 90) follow one another in the direction of the longitudinal axis (10) of the installation housing (2). Within each group (I, II, III) of battery cells (70, 80, 90), a flow path (50, 51, 52) for cooling air isformed, which flow path connects a feed air opening (35, 36, 46) for a cooling air flow (5, 6) to a cooling air outlet (20, 21, 23). In order to achieve effective cooling, first feed air openings (35) and a first cooling air outlet (20) are associated with a first flow path (50) in a first group (I) of battery cells (70) and second feed air openings (36) and a second cooling air outlet (21) are associated with a second flow path (51) in a second group (II) of battery cells (80). The cooling air flow (5) of the first flow path (50) is led to the first cooling air outlet (20) separately from the cooling air flow (6) of the second flow path (51) and the cooling air flow (6) of the second flow path (51) is led to the second cooling air outlet (21) separately from the cooling air flow (5) of the first flow path (50).