An electrochemical-cell stack assembly is provided. The assembly has an electrochemical-cell stack and a compression system that holds the electrochemical-cell stack in a state of compression. The compression system has a first endplate and a second endplate positioned at opposite ends of the electrochemical-cell stack. The compression system has a set of tension members coupled to the first endplate and the second endplate that maintain a fixed distance between the first endplate and the second endplate. The compression system has a compression plate disposed between the second endplate and the electrochemical-cell stack. The compression system has a compression member in contact with the compression plate, wherein the compression member is configured to transfer a force to the compression plate. The compression system has a locking nut fastened to the second plate. The locking nut secures the position of the compression member and compression plate relative to the second endplate.