Abstract: In order to ensure the continuous and reliable power supply of battery packs in critical power systems, and to solve the open circuit risk and system voltage loss caused by single battery failures, this paper takes the DC backup power supply of 220 kV substations as the application background. By designing an integrated single battery open circuit freewheeling device, an operation monitoring technology system covering fault identification, intelligent isolation, freewheeling guarantee, and charging protection is constructed. The effectiveness of the device in fault detection, bus voltage maintenance, and charging voltage regulation was verified using a modular architecture and multi parameter fusion criterion method, combined with a hardware experimental platform.