The Importance of Monitoring UPS Batteries: Lead-Acid and Lithium-Ion

Uninterruptible power supplies (UPS) perform a critical role within any environment they are deployed within and in particular server rooms and data centres, hospital and industrial facilities. Not only does the UPS provide an instantaneous source of reserve power from its battery set when the mains power supply fails, a UPS also provides a conditioned and regulated supply when mains power is present.

The most common type of energy reserve for a UPS system is a battery set. Smaller battery sets may be housed inside the UPS (internal) and larger ones or for larger UPS, they may be housed in an (external) battery cabinet or on a stand, which may be open or cladded (closed).

Whether the battery is of the lead acid (more traditional) or lithium-based, it will require monitoring and timely replacement during its working life. Failing to do so, will compromise the resilience of the UPS system itself and lead to load downtime.

The Critical Role of Batteries in UPS Systems

In data centre environments UPS systems bridge the gap between a mains power outage and the start-up of local backup power generators, and the then transfer back to mains power supply when utility power is restored.

When utility power is present, the UPS conditions and regulates the incoming voltage and frequency to remove sags, surges, brownouts, spikes and electrical noise, and charge the battery set.

The battery set may be wet or sealed lead acid (SLA) or lithium-ion batteries. Regardless, if the batteries fail then the UPS cannot perform its ‘uninterruptible’ role, leading to a load system and downtime. It is therefore vital to monitor the battery set both automatically with on-site testing, remotely and visually through annual inspections as part of a preventative maintenance routine.

Batteries also have specified design and working lives with windows for replacement. For example, a 5year design life lead acid battery should be replaced in years 3-4. A lithium-ion battery with a 10year design life, in years 7-8.

For more information see:
https://www.vertiv.com/en-emea/about/news-and-insights/articles/educational-articles/what-are-ups-batteries-and-why-are-they-so-critical/

Key Differences Between UPS Battery Types

Within a UPS system, batteries are consumable items that will require replacement at least one or twice during the working life of the UPS. This means that the longer the battery life, the less impact the battery set has on operational costs and overall sustainability.

Lead-Acid Maintenance-Free UPS Batteries

Lead-acid batteries, particularly sealed valve-regulated lead-acid (VRLA) maintenance free types, have been the standard in UPS applications for decades. This type of battery evolved from the battery used in standby power applications such as the automotive sector. Lead acid batteries are reliable, though with a relatively short working life of 3-4 years or 7-8 years dependent on their design life (5 or 10year).

Whilst maintenance free, lead acid batteries rely on chemical reaction between a hydrochloric acid electrolyte and lead plates to generate electricity. These materials degrade over time, lower the charge capacity available and hence leading to their need for replacement.

UPS Lithium-Ion Batteries

Lithium-ion (Li-ion) batteries are increasingly used in UPS systems due to their higher energy density, longer lifespan (8–15 years), lower weight, and better performance under demanding conditions.

This type of battery is installed with a more complex battery management system than with a lead acid battery. This may be built-into the UPS or installed as part of the UPS system. Whilst the battery monitoring system (and battery) is more advanced, lithium UPS batteries still require regular monitoring to ensure the UPS is resilient and can provide power from its energy reserve during an emergency.

Why Battery Monitoring is Critical to Prevent Downtime

There are several reasons for monitoring a battery.

Ensuring Reliability and Uptime

The primary purpose of a UPS is to prevent downtime during mains power supply failures. If a battery set fails unexpectedly, during a utility failure, the protected load crashes. Battery sets can also age and not be capable of delivering their calculated runtimes. This can again lead to system crashes during prolonged power outages.

Monitoring provides real-time information on voltage, temperature, state of charge, and state of health, ensuring engineers can proactively address problems before they result in outages. In industries like healthcare, finance, or data centers, even a few seconds of downtime can lead to catastrophic consequences.

Detecting Early Signs of Failure

Batteries degrade over time due to charge-discharge cycles, chemical changes, and environmental factors. Monitoring allows early detection of issues such as reduced capacity, individual battery block and battery cell imbalances, and increased internal resistance. An early warning system helps organisations schedule maintenance or replacements before failure occurs, preventing unplanned downtime.

Optimising Battery Lifespan

Both lead-acid and lithium-ion batteries are sensitive to charging regimes, temperature, and load profiles. Overcharging, deep discharging, or exposing batteries to high heat can drastically shorten their lifespan. For a lead acid battery, the design life can half for every one degree above 30°C.
Battery monitoring systems can track these variables, allowing operators to adjust environmental conditions and charging protocols to maximize lifespan and return on investment.

Cost Savings and Resource Optimisation

Replacing UPS batteries is a significant expense and can be up to 50% or of the initial UPS installation (dependent upon the battery size). For large-scale UPS installations, poorly monitored batteries can fail prematurely and if not identified early can lead to the rapid degradation of the entire battery set.
Monitoring extends battery life by ensuring optimal operating conditions and helps organisations replace batteries as part of a planned maintenance regime when necessary, avoiding wasteful premature replacements.

Compliance and Safety

In many industries, regulatory compliance requires demonstrating that critical infrastructure has a reliable backup system. Monitoring provides records and reports that help satisfy audits and compliance checks. Additionally, batteries, especially lithium-ion, can pose risks from overheating including thermal runaway and fire. Within a data centre environment, the latter is often cited as the reason against their adoption. Monitoring reduces these risks by ensuring batteries operate within safe parameters.

Supporting Predictive Maintenance

Monitoring transforms UPS maintenance from a reactive to a predictive model. Instead of waiting for failures or following a rigid replacement schedule, predictive maintenance uses real-time data trends to determine exactly when intervention is needed. For example, instead of replacement in year 8, a battery set could be of sufficient health to run for another year or two. This leads to greater efficiency, reduced maintenance costs, and higher reliability.

Preventing Theft

Whilst data centres tend to be highly secure sites, remote sites can be more exposed to the risk of unauthorised entry and potentially theft. For a remote site, such as a trackside or rural containerised deployment, the batteries and cables can present an opportunity to make money through recycling.

Battery Monitoring Tools

There are several ways to monitor UPS batteries.

The first is to rely on the UPS system itself. A UPS will constantly monitor electrical measurements and alarm when there is a deviation outside a present threshold. This alarm may just be front the front panel with an audible and/or visual indication or remotely via an SNMP, volt-free contact or BMS card. If the UPS has some sort of remote interface and can issue an email or SMS text alert, the site is not dependent upon someone responding to a visual or audible alarm locally. This approach works well with lead acid and lithium-ion battery packs.

The second is to put in place a dedicated battery monitoring system. This is more common in larger data centres where UPS and their battery sets have a dedicated room. PowerShield is a typical example of a complete battery monitoring system. This works well with lead acid and lithium battery packs for large UPS installations of 20kVA or more.

For either of the two above, additional temperature monitoring can be added via an environmental monitoring unit.

For smaller data centres, and remote sites the local running UPS sytems with lead acid battteries, built-in monitoring could be supplemented with intelligent battery sensors connected to an environmental monitoring system such as an AKCP sensorProbe+ SPX8 akcp-sensorprobex-spx8-environment-monitors. This type of battery sensors provides monitoring of battery voltage, temperature and current load and can be used to monitor generator start-up circuits, solar PV installations, uninterruptible power and DC power systems. The sensor can monitor individual battery blocks and strings. For smaller UPS systems with lithium-ion batteries, the battery management/monitoring system built-into the UPS is typically relied upon.

Conclusion

UPS batteries are the most critical component within a backup power system. Whether they the lead acid or lithium-ion type, the battery set requires regular monitoring and visual inspections, and replacement during the latter stages of their working life.

Monitoring UPS batteries is essential to ensure reliability, safety, cost efficiency, and regulatory compliance. While lead-acid and lithium-ion batteries have different characteristics, the principle remains the same: proactive monitoring transforms battery management from guesswork into a precise, data-driven process and one that can more accurately forecast when a battery set requires replacement or individual battery blocks are failing.