The short answer is: Data centers overwhelmingly use large, three-phase, online double-conversion UPS systems—but the specific architecture, battery chemistry, and redundancy configuration depend heavily on the facility's size, criticality, and power density requirements.
If you walk into a hyperscale facility, you will find megawatt-scale modular UPS systems paired with lithium-ion batteries. In a smaller colocation or enterprise data center, you may find conventional monolithic UPS units with valve-regulated lead-acid batteries. The common thread is that all of them are engineered for one purpose: to ensure that the IT load never sees even a millisecond of interruption, no matter what happens to the utility grid.
Here is a detailed look at the UPS technologies that power modern data centers.
The Dominant Topology: Online Double-Conversion
The overwhelming majority of data center UPS systems above 10 kVA use online double-conversion topology. In this design, incoming AC power is continuously rectified to DC, which charges the battery and feeds an inverter that converts it back to clean AC output. Because the inverter is always running, the connected load is fully isolated from utility disturbances—voltage sags, surges, frequency variations, and harmonics never reach the equipment. There is zero transfer time during a power outage; the battery simply takes over the DC bus, and the inverter continues without interruption.
This topology is the standard for data centers because it provides the highest level of power conditioning and protection. The trade-off is slightly lower efficiency compared to line-interactive designs, but for mission-critical facilities, the reliability justifies the cost.
Battery Chemistry: VRLA vs. Lithium-Ion
The battery is the heart of the UPS, and the choice of chemistry has a profound impact on lifespan, footprint, maintenance, and total cost of ownership.
Valve-regulated lead-acid (VRLA)** batteries remain the most widely deployed storage technology in UPS systems because of their low cost and well-characterized aging behavior. They typically last 3 to 6 years in data center service and require periodic internal resistance checks of every battery jar, often performed two to four times annually. VRLA batteries are also sensitive to heat: life halves for every 10°C increase above 25°C ambient temperature.
Lithium-ion batteries have reached an inflection point in data center adoption. As of 2025, lithium-ion captures approximately 40% of data center backup installations, with hyperscale facilities reaching 55% adoption. The advantages are substantial:
- Lifespan: Lithium-ion batteries last 10 years or longer, with designs targeting 15-year service life and up to 10 times the cycle life of VRLA.
- Space and weight: Lithium-ion UPS systems occupy approximately one-third the space of VRLA-based solutions and weigh 60–80% less.
- Recharge time: Lithium-ion achieves full charge in about two hours, compared to up to 24 hours for lead-acid.
- Temperature tolerance: Lithium-ion operates at temperatures up to 105°F (40°C), while lead-acid requires 68–77°F (20–25°C) ambient conditions.
- Maintenance: Lithium-ion batteries include battery management systems (BMS) that provide continuous monitoring of state of health and charge, reducing maintenance to annual inspections.
The total cost of ownership for lithium-ion over a 10-year period is approximately 39% lower than VRLA, despite an initial investment that runs 1.5 times higher. For AI and high-density deployments where rack space commands premium value, the density improvement translates directly to more compute per square foot.
Modular and Scalable Architecture
Modern data center UPS systems are increasingly modular and scalable. Rather than a single monolithic unit, a modular UPS is built around multiple independent power modules integrated into a single frame. This design offers several benefits:
- Pay-as-you-grow: Operators can purchase power modules as needed, reducing capital expenditure and adding capacity as demand grows.
- Redundancy: Modules can be configured for N+1 redundancy, so a single module failure does not affect the load.
- Serviceability: Faulty modules can be replaced without shutting down the entire system. Some systems offer "Live Swap" functionality for greater uptime.
- Scalability: A single frame can scale from a few hundred kilowatts to over a megawatt, and multiple units can be paralleled for multi-megawatt capacity.
For example, Schneider Electric's Galaxy VXL delivers 500–1250 kW in a single frame with a power density of up to 1042 kW/m², and up to 5 MW with four units running in parallel. Vertiv's Liebert APM2 offers capacity ratings from 10–150 kVA at 208V and 20–600 kVA at 480/415V, paralleling for a total system capacity of up to 2.4 MW.