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Knowledge is Power: Understanding UPS battery options

When it comes to the batteries within uninterruptible power systems (UPSs), one size doesn’t fit all.

In fact, for decades, most smaller standby systems have used sealed VRLA batteries, while larger double-conversion systems have typically relied on flooded-cell VLA batteries.

There’s also a relative newcomer to the family, as lithium-ion has joined the two decades-old siblings. Here, we break down the UPS battery family tree:

1. Valve Regulated Lead Acid (VRLA). Commonly referred to as sealed lead-acid (SLA) or maintenance-free, VRLA batteries are the most common type of UPS battery.

Lower upfront costs, relative safety, easy availability and minimal maintenance are the primary advantages of this battery. However, deeming VRLA batteries “maintenance-free” is slightly inaccurate, as they still require regular cleaning and testing.

On the downside, sealed batteries have a short lifespan of about 3 to 7 years. The term ‘valve regulated’ represents the manner in which gas is released from a VRLA battery; if pressure becomes too great, a valve will vent the gas.

Because heat is detrimental to this type of battery, their optimal environment is a dry, temperature-controlled area of 77 degrees or lower.

It is important to note that since water cannot be added to most VRLA batteries, anything that increases the rate of evaporation or water loss — such as temperature or heat from the charging current — will subsequently reduce the life of the battery.

a. Absorbent glass mat (AGM). AGM batteries are a subtype of VRLA batteries. In AGM batteries the electrolyte is held in woven glass fiber mats.
This design allows for flexibility of design, improved self-discharge rates, and a wider operational temperature range.
b. Gel Cell. The second VRLA subtype. Originally conceived during the early 1930s for use in portable electronics early gel cells were less likely to leak when handled roughly.
A modern gel cell uses an electrolyte mixture usually comprised of sulfuric acid mixed with pyrogenic silica resulting in a gel like substance.
Gel cells are known for increased tolerance to vibration, as well as allowing for the lower cost 1-12 Amp hour range VRLA batteries found in smaller UPS systems.

2. Vented Lead Acid (VLA). Also known as flooded or wet cell batteries, VLA not only boast exceptional reliability, but an average lifespan of 20 years.

Composed of thick, lead-based plates flooded with electrolyte acid, these batteries typically have higher upfront costs than their VRLA counterparts, as well as pose a number of safety concerns.

As a result, they require regular maintenance and careful handling because their liquid is corrosive and can be set off by forceful movement.

Wet cell batteries should only be used in areas with proper ventilation and must be adequately protected against vibration and shaking due to the possibility of liquid spilling. In addition, they are prone to damage in extreme climates as the water inside can evaporate or freeze.

Even though wet cell batteries require more maintenance and are more expensive to replace, they are a highly reliable power source for double-conversion UPSs.

3. Lithium-ion. The new kid on the block when it comes to UPS applications, lithium-ion batteries have matured significantly in recent years, both in their design and range of potential uses.

Lithium-ion creates a safe and stable alternative battery option for UPSs, with benefits that include longer lifespan, weight reduction, smaller footprint and expanded warranty coverage.

While originally deployed as battery cabinets in three-phase UPS installations, there are now smaller single-phase lithium-powered UPSs on the market.

Although this type of battery tends to be more expensive than the other two options — which is expected to change as adoption rates become more widespread — lithium-ion batteries offer lower long term operational expenses since they last longer.

While each of the three types of UPS battery has its own set of advantages and disadvantages, it is important to understand your options — not to mention, how to best manage and maintain them.

One battery pitfall to avoid at all costs is thermal runaway, a topic we explored in our last blog.

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