The invention resolves the problem of swelling of sealing electrochemical cells of prismatic format when they are assembled side by side in a grouping box by proposing a battery comprising at least two electrochemical cells (1a, 1b) of prismatic format, wherein the electrochemical cells are separated by a rigid wedge (2) having a hardness greater than or equal to 90 Shore A according to the standard ASTM D 2240 and by a flexible wedge (3) having a hardness of up to 60 Shore A according to the standard ASTM D 2240, the rigid wedge and the flexible wedge being electrically insulating.