This white paper outlines the importance of UPS battery maintenance and how to reduce the risk of premature battery failure.
Without a well-maintained, quality battery system that kicks into action when needed, a UPS system is practically worthless.
That’s why good battery care isn’t just desirable, it’s a downright necessity.
This whitepaper outlines the difference between a UPS battery’s design life and its service life. Even though many cells are said to have a 5 or 10-year design life, under EUROBAT (Association of European Automotive and Industrial Battery Manufacturers) guidelines a battery is considered ‘end of service life’ once its capacity falls below 80%.
This helps explain why it’s good practice to replace 5-year design life batteries at year 3 or 4. For 10-year design life cells, the recommendation is swap out in years 7-8.
What Factors Affect The Length Of UPS Battery Life?
Actual UPS battery service life depends on several factors, including:
- Temperature: sealed lead-acid cells perform best at 20-25oC. For every 10oC above this temperature, expected service life will halve.
- Frequency and depth of discharge: batteries are designed with a finite number of discharge and recharge cycles. Each discharge slightly reduces capacity, with partial discharges having less of an impact than full ones.
- Operating voltage: overcharging above the recommended rates can cause batteries to dry out. While undercharging leads to sulphate crystals forming on the plates, which harden and reduce battery capacity.
- Ripple current: AC ripple is one of the biggest causes of battery overheating, which speeds up deterioration in the battery poles.
- Poor storage of unused batteries: even unused batteries automatically discharge small amounts of energy. Cells stored for a sustained period should be top-up charged every few months and kept at a maximum temperature of 10oC.
The Most Common Problems With UPS Batteries
Here are some of the issues that can occur if a rigorous UPS battery maintenance regime isn’t followed:
- Grid corrosion: caused by the natural chemical reactions within the battery. Can lead to short circuits.
- Sulphation: sulphate crystals form within the electrolyte and at the battery plate terminals, resulting in a longer charging cycle.
- Short circuits: during battery discharge, plates can shed paste. Short circuits occur if this material contacts the battery plates.
- Dry out: overcharging increases the concentration of acid in the electrolyte. This releases gas, causing the battery to lose water. This can result in a decline in capacity over time.
- Thermal runaway: caused by increases in temperature, which in turn releases energy that produces a further rise in temperature. Can ultimately result in battery case meltdown and expose the grid.
- Top mossing: badly aligned separators and plates can form a crystalline moss, which leads to the cell self-discharging.
How To Prevent Premature UPS Battery Failure
The white paper concludes with some top tips about proactive UPS battery maintenance, battery monitoring, and battery testing.
The latter can cover the relatively simple i.e. manual visual and physical checks on a battery’s appearance). It could be impedance testing, which is a non-intrusive way of building up a ‘history’ of each battery cell that offers a broad indication of condition.
Or there’s discharge testing, also known as load bank testing, which tests the cells under normal and peak load conditions.
Finally, the document outlines the modern battery care systems incorporated into many modern uninterruptible power supplies.
These automatically test batteries and protect against ripple currents and slow discharges.