Rechargeable seawater batteries (SWBs) are regarded as sustainable alternatives to Li-ion batteries due to the use of an unlimited and free source of Na ion active materials. Although many approaches including the introduction of new catalysts have successfully improved the performance of SWBs, reconsidering the cell design is an urgent requirement to improve the performance and scale up the production of practical batteries. In this study, by adjusting the maximum space efficiency, a rectangular cell is developed which due to its unique architecture, benefits from optimized contact to improve the overall charge transfer in the system. In view of the rigidity of the solid electrolyte, the novel cell model is intended to have adequate flexibility to be easily transported and practically utilized. Furthermore, the enhanced efficiency of the parallel stacked modules, indicates the capability of this cell in practical use. The designed catalyst-free cell system shows a record capacity of 3.8 Ah (47.5 Ah kg−1), energy of 11 Wh (137.5 Wh kg−1), and peak power of 523 mW for individual unit cell, while it also retains performance up to 100 cycles. This design paves the way for commercializing rechargeable seawater batteries.