Battery Multiple Units: A Techno-Economic Analysis of Development Pathways

In the policy context of achieving carbon neutrality, decarbonization has become a key objective for the UK railway system. Although overhead line electrification (OLE) remains the main approach, its high infrastructure cost has led to delays and cancellations of many projects. Battery multiple units (BMU) are a promising alternative, yet their large-scale adoption is limited by battery energy density and long charging times. This study develops a unified techno-economic modelling and optimization framework for three primary BMU energy supply modes: fast charging, intermittent electrification, and battery swapping. The proposed framework minimizes system-level costs and identifies, through case-based analysis, the boundary conditions under which each mode is most cost-effective. A case study on the UK East West Rail project shows that the battery swapping mode provides the greatest techno-economic advantage, reducing investment cost by 72.8% compared with the overhead line electrification solution. Fast charging, intermittent electrification, and battery swapping are found to be most suitable for short, medium, and long-distance operations, respectively. The findings offer data support and theoretical basis for future deployment of BMU trains to achieve efficient and cost-effective railway decarbonization.