We explore the importance of proactive UPS battery care plays in reducing the risk of premature failure.
UPS batteries are the often unsung hero of uninterruptible power supplies. Without a properly functioning battery set, the power protection provided by a UPS system is rendered useless.
But batteries can be temperamental. There are lots of factors that can impact on their service life. And they’re amongst the UPS components most likely to fail.
Riello UPS’s Technical Services Manager Jason Yates speaks to Electrical Review magazine about the proactive steps data centre and other site operators can take to look after their precious batteries and ensure they perform when needed most.
The UPS battery care article begins by explaining the subtle difference between a battery’s design life and its service life.
With the former, a 10 year design life battery will technically last for a full 10 years, assuming perfect operating conditions.
But as we all know, there’s no such thing as a “perfect” installation or conditions. UPS batteries are said to be at the end of their useful service life when their capacity falls below 80% of the original sum.
As Jason explains, that’s why it’s common practice to swap out 10 year design life batteries at year 7 or 8 (year 3 or 4 for 5 year design life).
This takes into account any reduction in capacity while also leaving a big enough margin of error against a more serious failure.
Aspects Affecting UPS Batteries & What Can They Cause?
High temperatures tend to be the biggest cause of premature battery failure. Sealed lead-acid (SLA) cells – the most common type of UPS battery – work best at ambient temperatures of 20-25oC.
Industry best practice suggests that for every 10oC above this optimal level, battery service life drops by 50%. So if your UPS and batteries are constantly in a room topping 40oC, then you’ll need to replace them much earlier than the recommended guidance.
How often a battery is discharged and the depth of discharge is also important as they have a finite number of charge/recharge cycles. Every discharge slightly reduces battery capacity. While partial discharges have less impact than fully discharging the battery.
Jason highlights some of the other factors that will affect batteries, including over and undercharging. The former generates excess gas that will dry cells out. While the latter can lead to sulphate crystals on the plates that harden over time and reduce capacity.
He also goes on to describe some of the most common conditions found in UPS batteries. These include sulphation, which increases internal resistance and leads to a longer charging cycle.
Thermal runaway is another such condition. This occurs when an increase in battery temperature has a knock-on effect of releasing energy that leads to a further temperature increase.
Emphasis On Maintenance, Monitoring & Testing
Jason’s UPS battery care advice article concludes with some recommendations to reduce the risk of premature battery failure.
An obvious start is a proactive UPS battery maintenance regime. At a minimum this would involve an annual physical inspection of all batteries to check for any signs of corrosion, cracking or swelling. Engineers would also clear any debris and tighten the inter-cell connections.
The piece goes on to talk about the benefits of battery monitoring as well as the battery care systems incorporated into many modern UPS power systems.
It finishes with an overview of the range of battery testing available. First up, there’s impedance testing. This only offers a broad indication of battery condition, but its main advantage is that it is a non-invasive process so it doesn’t require the batteries to go offline.
A more comprehensive option is discharge testing, often called load bank testing. This examines the cells at both normal and peak load conditions. Its major drawback is that it does take the batteries offline.
While in most cases this is for less than 24 hours, in some circumstances the batteries are out of commission for several days.
That’s why there’s a third option which offers something of a halfway house. Partial discharge testing discharges the batteries by as much as 80%.
While this inevitably reduces their availability, it does mean if there’s an issue with the mains supply, the UPS still has 20% capacity active as a safety net.
And with partial discharge testing, batteries should be fully available again within 8 hours.
