Abstract Diesel-electric locomotives remain the backbone of freight rail transport in Zambia. However, ageing fleets operating under low-speed duty cycles suffer from high fuel consumption and inefficient dissipation of braking energy. This paper investigates a battery-assisted hybridization strategy focused on regenerative braking energy recovery for Zambia Railways Limited (ZRL) diesel-electric locomotives operating along the 890 km Kitwe–Livingstone corridor. A MATLAB/Simulink co-simulation framework integrating traction demand, route gradients, battery dynamics, diesel fuel mapping, and a rule-based energy management strategy is developed and calibrated to ZRL operating conditions. A 7.5 MWh lithium iron phosphate (LFP) Battery Energy Storage System (BESS) installed on a tender wagon is evaluated based on realistic regenerative energy availability and State-of-Charge constraints. Simulation results indicate that regenerative braking capture and traction power smoothing reduce diesel fuel consumption by 15.4% per trip. The associated fuel cost savings demonstrate economic viability under conservative assumptions and can be reinvested into rail infrastructure and rolling stock maintenance, supporting improved operational reliability. The findings show that regenerative hybridization alone offer a practical, infrastructure-light pathway for improving energy efficiency and reducing fuel dependence on moderate-gradient freight corridors in developing railway networks. Keywords Diesel-Electric Locomotives, Battery Energy Storage (BESS), Traction Energy Recovery, Hybrid Locomotive Retrofit, Regenerative Braking, Energy Management System, MATLAB/Simulink.