An electrochemical cell system (10, 100) comprising: a plurality of electrochemical cells configured to operate in both fuel cell mode and electrolyzer mode, the plurality of electrochemical cells arranged in an electrochemical cell stack (12, 102-106), said electrochemical cell stack including a plurality of substacks (14, 16, 18, 108-124) having at least a first substack (14, 108) and a second substack (16, 110); and a first electrical control device (20, 132) electrically coupled to said first substack (14, 108) of said plurality of substacks (14, 16, 18, 108-124) to selectively electrically reconfigure said first substack to operate electrically between a series and a parallel configuration or a combination of the two with other substacks of said plurality of substacks; a second electrical control device (22, 134) coupled to the second substack (16, 110) of said plurality of substacks, and wherein said substacks (14, 16, 18, 108-124) of said plurality of substacks are configured such that fluid flows in series from substack to substack of said plurality of substacks (14, 16, 18, 108-124), wherein: the electrochemical cell system (10, 100) further comprises a second electrochemical cell stack that includes a plurality of electrochemical cells arranged into a plurality of substacks, wherein fluid flows in series from substack to substack of said second electrochemical cell stack; a single flow control point is arranged to control the fluid flow equally through both said electrochemical cell stack (12, 102) and said second electrochemical cell stack without separate fluid flow controls; and said first substack is electrically coupled with a first substack of said second electrochemical cell stack, and wherein said second substack is electrically coupled with a second substack of said second electrochemical cell stack. a plurality of electrochemical cells configured to operate in both fuel cell mode and electrolyzer mode, the plurality of electrochemical cells arranged in an electrochemical cell stack (12, 102-106), said electrochemical cell stack including a plurality of substacks (14, 16, 18, 108-124) having at least a first substack (14, 108) and a second substack (16, 110); and a first electrical control device (20, 132) electrically coupled to said first substack (14, 108) of said plurality of substacks (14, 16, 18, 108-124) to selectively electrically reconfigure said first substack to operate electrically between a series and a parallel configuration or a combination of the two with other substacks of said plurality of substacks; a second electrical control device (22, 134) coupled to the second substack (16, 110) of said plurality of substacks, and wherein said substacks (14, 16, 18, 108-124) of said plurality of substacks are configured such that fluid flows in series from substack to substack of said plurality of substacks (14, 16, 18, 108-124), wherein: the electrochemical cell system (10, 100) further comprises a second electrochemical cell stack that includes a plurality of electrochemical cells arranged into a plurality of substacks, wherein fluid flows in series from substack to substack of said second electrochemical cell stack; a single flow control point is arranged to control the fluid flow equally through both said electrochemical cell stack (12, 102) and said second electrochemical cell stack without separate fluid flow controls; and said first substack is electrically coupled with a first substack of said second electrochemical cell stack, and wherein said second substack is electrically coupled with a second substack of said second electrochemical cell stack. the electrochemical cell system (10, 100) further comprises a second electrochemical cell stack that includes a plurality of electrochemical cells arranged into a plurality of substacks, wherein fluid flows in series from substack to substack of said second electrochemical cell stack; a single flow control point is arranged to control the fluid flow equally through both said electrochemical cell stack (12, 102) and said second electrochemical cell stack without separate fluid flow controls; and said first substack is electrically coupled with a first substack of said second electrochemical cell stack, and wherein said second substack is electrically coupled with a second substack of said second electrochemical cell stack.