A connecting element electrically and mechanically connects two electrolytic cell stacks. An electrolysis device includes at least one connecting element of this type and the electrolytic cell stacks are connected by the connecting element. For the hydraulic connection of the electrolytic cell stacks, the connecting element has at least two hydraulic interfaces for each of two water circuits, which water circuits are independent of each other. Furthermore, the connecting element has electrical connection points electrically connected to each other, in order to connect the electrolytic cell stacks in a common circuit. By the connecting element, the connected electrolytic cell stacks can be hydraulically separated or connected to each other, depending on the design.