Abstract: A smart mobile DC power supply device has been developed to address the issues of low efficiency, high operational risk, and complex operation of traditional DC power transition methods during the replacement of battery packs in substations, in order to enhance the reliability and emergency support capabilities of DC system operation. The device adopts an integrated structure combining a backup battery pack, a high-frequency charging module, and an intelligent monitoring system, supporting multiple input modes such as mains power and generators. It has functions such as mobile portability, intelligent charging and discharging control, and multiple electrical protections, and can achieve fast access and uninterrupted power supply. Practical application has shown that the device effectively shortens the battery pack replacement time by about 50%, significantly reduces on-site operation intensity and safety risks, and ensures the continuous and reliable operation of the DC system in emergency situations. This intelligent mobile DC power supply device has good practicality, safety, and economy, and has promotional value for improving the operation and maintenance level of DC systems in substations.