Modular batteries offer substantial advantages to battery energy storage applications, including prolonged battery lifespan and enhanced fault-tolerance. Focusing on DC structures, scalable battery power modules can be interconnected in series and/or in parallel in order to adjust the capacity and voltage of the battery system to the requirements of the application. Selecting the optimal modular configuration is crucial for maximising the advantages of modularity. Therefore, this article presents a methodology designed for evaluating the fault-tolerance and reliability of all possible battery configurations, and provides a comparative analysis including also the controllability, flexibility and voltage amplification capability factors. The Parallel configuration is identified as the optimal solution for low voltage applications. Nevertheless, due to its low amplification capability, the Parallel-Series architecture should be adopted for applications with higher voltage requirements. In this regard, efforts should focus on maximising the number of parallel connected battery power modules, employing a high-gain DC-DC converter.