Unified Facility Criteria (UFC) 3-520-05 provides design criteria for stationary secondary battery installations. These batteries are operated on a continuous float charge and may require ventilation to limit hydrogen gas concentrations. This UFC also addresses lithium-based batteries that are stored or charged inside facilities. This UFC serves as a planning, engineering, and design reference for professional facility planners, designers, and constructors, including DoD personnel and Government contractors. Designers and planners will use this document for individual project planning, for preparing engineering documentation, and for preparing contract documents for construction and renovation projects.