Updated 07 March 2025
When it comes to Uninterruptible Power Supply (UPS) systems, batteries play a crucial role in ensuring continuous power backup. Choosing the right battery type, understanding battery capacity, and following best practices for maintenance can significantly impact performance and longevity. This guide covers everything you need to know about UPS batteries, including different types, battery capacity calculations, safety precautions, and maintenance tips.
Standby Systems offers a wide range of batteries, including vented flat plate, Plante, and tubular technology cells. We also provide Valve Regulated Lead Acid (VRLA) batteries, often mistakenly referred to as sealed lead acid (SLA) or semi-sealed lead acid. Our selection includes lead-carbon VRLA for high-cycle applications, high-temperature and deep-cycle VRLA, and high-rate, long-life (HRL) VRLA for UPS use. Additionally, we offer nickel-cadmium batteries to meet various power needs.
Types of UPS Batteries
The most used and widely mass-produced battery for UPS applications is the lead-acid battery. It is favored for its reliability, cost-effectiveness, low maintenance (VRLA), and offers ease of recyclability.
Next up, you will find more information about the most common battery types.
Note: You will see the words “Design life” and “Actual achieved service life” in the points below. There are many reasons why batteries don’t often achieve their design life. This will be discussed in greater detail later in this article.
Valve Regulated Lead Acid (VRLA) Batteries, also called SLA
Design life 3 to 5 years: SP VRLA battery, 12V AGM Lead acid battery, EPS battery, lead acid battery, Sacred Sun Green Energy Solution Provider, and UPSEL VRLA battery.
Design life 10 years or 12 years: SP/SPG High power battery, AGM battery, Sacred Sun Green Energy Solution Provider and ELITE ELGHR high rate batteries.
Design life 15 years: HRL 12V AGM Lead acid battery, EPS battery, lead acid battery, Sacred Sun Green Energy Solution Provider or ELITE ELHRL High-rate long-life battery.
Actual achieved service life in a float application: 2 to 4 years (for shorter-life versions), 6 to 8 years (for longer-life versions), and 10 to 15 years for SPG/HRL.
Features
- Individual cells are sealed with high-pressure valves to minimize gassing and reduce water loss.
- Uses Absorbed Glass Mat (AGM) technology, eliminating free-flowing electrolyte, also referred to as starved electrolyte technology.
- Mass-produced and easily available off the shelf at a low cost, therefore the most affordable.
- Proven technology so you know what you are buying for your money.
- Low maintenance, never requires an electrolyte top-up, has a small footprint, and is easily recyclable.
Standby System’s recommended brands: UPSEL and ELITE ELGHR and ELHRL
Other brands that are also popular and available from Standby Systems on request are:
CSB, DELKOR, DELCO, RITTAR, VISION, CHLORIDE & EXIDE, and ENERSYS.
2. Vented Lead Acid (Flooded) Batteries
Design Life: Up to 20 years
Actual achieved service life in a float application: Matches design life.
Features
- Requires regular air exchange due to high levels of hydrogen gas venting.
- Very High maintenance and requires a larger footprint and specially designed battery rooms.
- Corrosive to its installed environment.
- Very expensive with long delivery periods as they are only made on order and not a stock item.
- Requires special charging regimes and specialized battery charging equipment.
- Easily recyclable.
Standby System’s recommended brands: First National Battery, Sacred Sun, Enersys Sonnenschein, Hoppecke.
3. Maintenance-Free (MF) Lead Acid Batteries (Also referred to as SMF)
Design Life: 3 to 5 years
Actual Life on Float Service: 3 to 5 years
Features
- Wet cells that vent hydrogen gas and leak large amounts of acid if a cell cracks.
- Primarily designed for automotive use.
- Cheap to buy so often wrongly used in UPS applications.
Standby System’s recommended brand: We don’t recommend their use in UPS applications.
NOTE: Standby Systems does not sell Lithium technology batteries due to their severe environmental impact, ethical concerns in raw material sourcing, and lack of technical advantage in UPS applications. Lead-acid batteries remain the superior choice, as they are 100% recyclable in South Africa and better suited for UPS operation. Click here to read more on this topic.
And speaking of batteries that we DON’T recommend…
Why Standby Systems Does NOT Use Car Batteries in UPS Applications
Standby Systems does not use car batteries in UPS applications because they are designed for cranking rather than deep discharge, making them unsuitable for sustained power backup. Their lifespan is significantly shorter when used in UPS systems, leading to frequent replacements and higher maintenance costs. Additionally, car batteries perform poorly in float charge conditions, which are essential for reliable UPS operation. This results in an increased risk of failure and unexpected downtime. Safety is another major concern, as car batteries are not built to handle the continuous charging and discharging demands of a UPS. Ultimately, while they may seem like a cheaper option upfront, they are not cost-effective in the long run due to their frequent failures and replacements.
Unlike VRLA batteries, most car batteries are vented lead-acid types that release hydrogen gas during charging. This creates a risk of gas buildup in enclosed spaces where UPS systems are typically kept. Also, the risk of acid spills and leaks is much higher with car batteries.
Standby Systems only supplies high-quality VRLA batteries specifically designed for UPS applications. These batteries offer long service life, excellent float charge performance, reliable deep discharge, and enhanced safety features, ensuring uninterrupted power when you need it most.
How to Calculate UPS Battery Capacity
To ensure uninterrupted power during outages, selecting the right battery capacity is essential. A battery capacity calculator helps determine the required ampere-hour (Ah) capacity for a given load and duration.
Calculate Battery Capacity
Example
If the current drawn is 33A and the backup time required is 2 hours 45 minutes:
Ah drawn = 33A × 2.75 hours = 90.75 Ah
Since lead-acid batteries are rated at a 10-hour discharge rate, and efficiency varies, an IS standard efficiency factor of 71.7% applies:
Required Battery Capacity = 90.75 Ah / 0.717 = 127 Ah
Thus, selecting a 130Ah battery would be ideal for the application.
Because a UPS battery is a high-rate battery, it is crucial to consider the power per cell (watts per cell) in discharges of up to 30 minutes. Some manufacturers may sell a 100Ah battery with only 290 watts per cell for 15 minutes, whereas the ELGHR ELITE from Standby Systems delivers 340 watts per cell at 98Ah. Always check the battery’s performance data carefully to ensure it meets your power requirements.
Why Do Some UPS Batteries Explode or Catch Fire?
Lead-acid batteries generate hydrogen and oxygen gas during charging. Overcharging or poor ventilation can cause gas buildup, leading to explosions if ignited by a spark.
If a VRLA battery is operated in a very dirty environment, the valves in the lid can block up. If this occurs, the pressure inside the battery will continue to increase with the charging gasses that are given off, eventually causing the casing to explode.
As batteries get older, their internal impedance gets higher, meaning they will need a higher charge current, which has the added effect that more heat is generated inside the cell. Higher temperatures lead to increased gassing and water loss. In VRLA batteries, this accelerates drying out, eventually rendering the cell unable to produce power. In older batteries nearing the end of their lifespan, excessive heat and lack of maintenance can even result in a fire hazard.
Key causes include:
- Sparks near charging batteries
- Frayed battery cables
- Blocked vent plugs
- Poor quality chargers causing overcharging
- Hydrogen accumulation in enclosed spaces
- PSOC (Partial State of Charge Discharges), i.e., discharging a battery when it is not fully charged.
Prevention Tips:
- Ensure proper ventilation in battery rooms
- Keep vent plugs clean and unclogged
- Use insulated tools to prevent accidental sparks
- Regularly inspect cables and connectors for damage
- Use high-quality chargers with voltage regulation
State of Charge (SOC) and Battery Health
SOC indicates how much charge remains in a battery, typically expressed as a percentage. Monitoring SOC helps optimise battery performance and longevity.
How to Measure SOC in Lead-Acid Batteries
Voltage Method: Measure open circuit voltage and compare it to a reference chart.
Impedance testing: Measure the internal impedance of a battery in a fully charged state and the temperature and compare to the manufacturer’s reference data. (Particularly useful with VRLA AGM technology).
Specific Gravity Measurement: Use a hydrometer to check electrolyte density (for flooded batteries).
Five UPS Battery-health Maintenance Tips
- Avoid deep discharges that reduce battery life.
- Buy a UPS with intelligent battery test facilities and alarms and ensure that it can deliver the required recharge current that your selected battery will need.
- Charge batteries regularly and avoid prolonged storage in a discharged state.
- Don’t let batteries discharge to end voltage and then switch off and stay in that state for more than 24 hours, or sulphation will occur, permanently damaging the battery and its performance and life.
- Keep batteries at stable temperatures, avoiding extreme heat or cold.
Advantages and Disadvantages of Lead Acid Batteries
Advantages
- Reliable and cost-effective – VRLA.
- Always easily available – VRLA.
- Proven technology with over 160 years of development.
- High recyclability (97% of materials can be reused) in South Africa
- Safer than lithium-ion batteries.
- High cycling ability – Lead carbon and Tubular technologies.
Disadvantages
- Heavy due to lead composition.
- Slower charging compared to lithium-based alternatives.
- Lithium ion contains rare earth minerals, including cobalt, selenium, and Cadmium, which are highly toxic.
There is currently no lithium battery recycling plant in South Africa, with the nearest facility located in France. Disposing of end-of-life lithium batteries is extremely costly, as they are classified as hazardous goods. This requires expensive specialized shipping—often in a dedicated container—and additional fees paid to the recycling plant, as lithium battery recycling is not yet economically viable.
Why Lead Acid Batteries Are a Preferred Choice
Despite the rise of lithium-ion and LFP batteries, lead-acid batteries remain widely used in 99% of UPS applications due to their affordability, off-the-shelf availability, ease of shipping all over the world, robustness, and ease of recycling. With advancements like enhanced flooded batteries (EFB), VRLA AGM starved electrolyte technologies, and ultra-battery technology, lead-acid batteries continue to evolve, offering improved performance and lifespan.
Conclusion
Selecting the right UPS battery involves understanding different battery types, calculating the required capacity, and following best practices for maintenance and safety. Whether choosing VRLA, vented, or LiFePO4 batteries, ensuring proper handling and monitoring will maximise performance and reliability.
If you want to know more about UPS batteries and how Standby Systems can help you match the right battery with your UPS unit, contact us.
Visit Standby Systems’ website or contact us at 011 794 3406 for services, 011 794 2541 for UPS systems for sale, or our UPS contact number at 082 450 2361.