In order to solve the problems of the subsea template was frequently lifted to the deck to replace the battery due to insufficient battery capacity， during the deep-sea exploration of the ship HYSY 708， a 3000m off-line battery distribution manager was designed and manufactured. The system is mainly composed of control cabin， deep-water battery pack， watertight cable， etc.， which can independent complete the power management and output of 4 deep-water battery packs. Made of high-strength aluminum alloy， the system can withstand pressure not less than 30MPa， Using PLC as the core controller， the control program is written. Through laboratory experiments， the control function is verified， and the switch of battery pack can be realized stably. In May 2023， the field application was carried out in the depth of 1800m in a certain sea area of the South China Sea， and the underwater operation time of the subsea template was successfully increased from about 3 days to more than 10 days， greatly extending its working time in the seabed， saving valuable working time for the ship HYSY 708， and successfully assisting the ship to complete the survey task.