The invention relates to a device for storing electrical energy (1), especially for a motor vehicle. Said device comprises a plurality of flat cells (2) that are stacked one on the other with their flat sides substantially in parallel, the flat cells defining at least one first stack (3). A cooling element (5) is arranged between adjacent flat cells of the at least one first stack. The invention is characterized in that the cooling element has at least one opening (6) into which a heat transfer element (7) is inserted.