This recommended practice provides guidance for the design of the dc auxiliary power systems for nuclear and non-nuclear power generating stations. The components of the dc auxiliary power system addressed by this recommended practice include lead storage batteries, static battery chargers, and distribution equipment. Guidance for selecting the quantity and types of equipment, the equipment ratings, interconnections, instrumentation, control and protection is also provided. This recommended practice is intended for nuclear and large fossil-fueled generating stations. Each recommendation may or may not be appropriate for other generating facilities; e.g., combustion turbines, hydro, wind turbines, etc. The ac power supply (to the chargers), the loads served by the dc systems, except as they influence the dc system design, and engine starting (cranking) battery systems are beyond the scope of this recommended practice.