Microstructures and electrochemical characteristics of La0.7Ce0.3Ni4.2Mn0.9−x Cu0.37(Fe0.43B0.57) x (x = 0–0.20) hydrogen storage alloys are investigated. X-ray diffraction and backscattered electron results indicate that the pristine alloy is single LaNi5 phase while the alloys containing Fe0.43B0.57 consist of LaNi5 matrix phase and La3Ni13B2 secondary phase. The relative abundance of La3Ni13B2 phase increases with the increase in x value. The a and V of LaNi5 phase increase with increasing x value. Activation property of the alloy electrodes is improved by substituting Mn with Fe0.43B0.57. Maximum discharge capacity of the alloy electrodes monotonically decreases from 323.3 mAh g−1 (x = 0) to 311.3 mAh g−1 (x = 0.20). Cycling capacity retention rate at the 100th cycle decreases from 79.3% (x = 0) to 68.2% (x = 0.20) with increasing x value, which is ascribed to the degradation of corrosion resistance. High-rate dischargeability of the alloy electrodes first increases with increasing x from 0 to 0.10, and then decreases until x increases to 0.20. It demonstrates that the substitution of Mn with Fe0.43B0.57 is an effective approach to improve the overall electrochemical performances of the Co-free high-Mn alloy electrodes.