A sub-stack assembly 100 of a number of cells 102 bonded together with thermoplastic film 104 is disclosed. Each of the individual cell components are bonded to one another with thermoplastic film 104. A number of sub-stack assemblies 100 are stacked and sealed relative to one another by a soft compliant gasket seal 106, such as a foam rubber or other suitable materials. As a result, only one soft foam rubber seal 106 would be required for each sub-stack assembly 100 rather than for every cell.