A UPS room is unusual because it houses two hazards that require incompatible responses in the same enclosure. The UPS modules themselves are a Class C power electronics hazard: rectifiers, inverters, capacitors, and control electronics where a fault ignites insulation and where clean agent is the appropriate answer because it extinguishes without destroying the equipment.
The battery plant is a different problem entirely. Valve-regulated lead acid strings generate hydrogen during charging and particularly during overcharge or thermal excursion, which introduces an explosive atmosphere requiring ventilation rather than suppression. Lithium-ion batteries, now common in UPS installations for their footprint and cycle life advantages, introduce thermal runaway, which is a fundamentally different phenomenon from a fire.
Thermal runaway is the crux. A lithium cell in runaway is generating its own heat and its own oxidizer internally through exothermic decomposition, which means it does not require ambient oxygen to continue and cannot be extinguished by displacing it. A clean agent system will suppress flaming combustion in the room and the cell will keep escalating, propagate to its neighbors, and vent flammable electrolyte gas that can accumulate and deflagrate. NFPA 855 requires explosion control for exactly this reason, and it is the single most commonly missing element in installations that otherwise look well protected.