Battery Technology for Data Centers and Network Rooms: VRLA Reliability and Safety

Posted by on June 20, 2012

White Paper 39

Valve regulated lead acid (VRLA) batteries have been used in UPS systems for almost 20 years. Compared to traditional flooded cell solutions, VRLA batteries allow higher power density and lower capital costs. VRLA batteries are typically deployed within power systems smaller than 500 kVA. Features of a VRLA battery include:

  • Container is sealed; liquid cannot be added or removed
  • Contains lead plates in a solution of sulfuric acid diluted in water (electrolyte)
  • Electrolyte is immobilized (not allowed to flow)
  • Operates at high currents
  • Safety vents allow escape of gas only under fault or excess charging conditions
  • Oxygen & hydrogen are recombined internally to form water
  • Installed in open frames or large cabinets (or embedded inside small power systems)

This paper will explore in greater detail some of the operating considerations of the VRLA battery. Concerns about VRLA batteries generally center on two issues: reliability and safety. Because of their wide usage (deployed at an estimated rate of 10 million units per year), many people have had experience – both good and bad – with VRLA technology. To better understand both the extent as well as the limitations of VRLA technology, we first need to understand the variations in VRLA design and the theory of operation. We can then look at the application and misapplication of this technology. All products eventually come to an end of useful life. We will explore when that should be in a VRLA battery and how that life could be lengthened or shortened according to its application and care. Although catastrophic failures are rare, we will look at what safety hazards are possible when VRLA batteries are misapplied or misused.

“Battery Technology for Data Centers and Network Rooms: VRLA Reliability and Safety” Full White Paper (Click Here To Download)

Executive Summary:

The valve regulated lead-acid (VRLA) battery is the predominant choice for small and medium sized uninterruptible power supply (UPS) energy storage. This white paper explores how the technology affects overall battery life and system reliability. It will examine the expected performance, life cycle factors, and failure mechanisms of VRLA batteries.


  • VRLA types
  • VRLA theory of operations
  • VRLA life expectancy
  • Failure modes
  • Safety
  • Handling and environmental safety


When properly applied and maintained, VRLA batteries and cartridges such as those used in small and medium-sized UPS systems can give reliable performance for three to five years or longer (depending upon battery selection). Battery dry-out is a major cause of VRLA battery end of life. Continuous monitoring and control systems can detect and respond to conditions that could cause premature cell failure. Temperature compensated and current limited charging can help prevent thermal runaway. Use of redundant, parallel strings can reduce the consequences of a cell failure and increase the life of a battery system.

VRLA batteries are safe to use in data centers and network rooms when properly applied and maintained. Neglect, abuse, or improper application can create conditions that could push a battery into failure mode. In extreme cases, catastrophic failure can cause fire and/or release of hazardous gases. Proper cooling and ventilation, regular monitoring, use of parallel strings, and temperature compensated charging can all contribute to long battery life and safety.

White Paper Written By:

Stephen McCluer is a Senior Manager for external codes and standards at Schneider Electric. He has 30 years of experience in the power protection industry, and is a member of NFPA, ICC, IAEI, ASHRAE, The Green Grid, BICSI, and the IEEE Standards Council. He serves on a number of committees within those organizations, is a frequent speaker at industry conferences, and authors technical papers and articles on power quality topics. He served on a task group to rewrite the requirements for information technology equipment in the 2011 National Electrical Code.

Universal Networking Services’s partnership with Universal Power Group, Inc. has enabled us to build a strong distribution network of battery and related power components that meet consumer needs for accessibility, portability, security and mobility, coupled with value added offerings such as battery pack assembly and battery replacement/recycling programs.

Please feel free to contact us if you have any questions regarding this topic.

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