VRLA Battery | Working, Benefits & Limitations

Valve Regulated Lead Acid (VRLA) batteries are sealed, maintenance-free lead-acid batteries that prevent leaks and require no ventilation.

Unlike flooded lead-acid batteries, they can be installed in any orientation, offering reliable, long-lasting, and efficient power for backup systems, solar setups, and industrial applications.

Table of Contents

What is VRLA Battery?

The full form of VRLA Battery is Valve Regulated Lead-acid Battery. A VRLA battery or Valve Regulated Lead Acid Battery is a sealed battery or maintenance-free battery. This is one type of Lead-acid rechargeable battery. The VRLA Battery does not require stringent ventilation.

Also, we can mount the battery in any orientation. The reduced ventilation requirement is an added advantage of VRLA. The VRLA battery occupies less mounting space and moderate room ventilation. The VRLA battery is the most popular reserve power design because;

The electrolyte is captive, preventing it from spilling even when its case is punctured.
VRLA batteries are “maintenance free” and it does not require additional electrolyte or water.

Problems of Flooded Lead-acid Battery

When the lead-acid battery charging is near completion, hydrogen (H2) gas liberates at the negative plate. Similarly, at the end of battery charging, oxygen (O2) gas liberates at the positive plate. Hydrogen gas is released before mixing with water inside the battery. It happens because the reverse process of battery discharging to charging is not perfect.

To prevent the build-up of the explosive hydrogen gas, a battery has a vent to release the pressure. The electrolyte may spill out from the vents with tilting of the battery. This is a hazard during the shipping of the batteries and makes the battery unsuitable for many applications. Also, proper ventilation is required in the room.

Furthermore, the constant loss of Hydrogen leads to a reduction of water in the electrolyte. And, the battery needs lost water replenishment by opening the battery vent plug and topping up DM water.

Why VRLA Battery is better than flooded lead Acid Battery

The valve-regulated lead-acid batteries hinder the movement of the electrolyte inside the battery container and trap the hydrogen gas near the plates. This process makes readily available hydrogen gas for re-combination during battery charging.

This type of construction greatly reduces water loss during the charging and discharging cycle. Thus, this technology makes the battery sealed and maintenance-free (no need to add water).

This is the reason why we can use VRLA batteries in any position or orientation. There is no possibility of electrolyte spillage in VRLA. Also, no water needs to be added to the electrolyte in VRLA sealed maintenance-free batteries.

We use VRLA batteries for applications that require a large amount of energy storage at a lower cost. They are used in large portable electrical devices, off-grid power systems, and similar roles.

How does Valve Regulation Function in VRLA Battery?

During rapid recharging, the electrolyte may boil and pressurize the battery case. The gas build-up may be too rapid for recombination to mix with oxygen to form water. These effects require valve regulation, normally in the form of a one-way pop-off valve. The valve opens in case of pressure build-up.

The immobilizing agent prevents acid leakage when the valve pops. VRLA battery has a pressure relief valve that activates when the battery starts building pressure of hydrogen gas. This is generally a result of being recharged at excessive voltage, typically greater than 2.30 volts per cell.

Valve activation allows some of the gas or electrolyte to escape. As a result, the overall capacity of the battery decreases. Therefore, the charging current of the VRLA battery shall not exceed the specified value recommended by the manufacturer.

Protection in VRLA Battery

The electrolyte may produce too much pressure
The hydrogen gas build-up may be too fast for recombination with the water

To regulate these events, a one-way pop-off valve is incorporated into the battery body, which only opens when the pressure builds up. The immobilizer used in these batteries ensures that there is no spillage or leakage of the liquid inside.

Benefits of VRLA Batteries

Safety: Designed to prevent leaks and minimize the risk of spillage, ensuring safe operation in various environments.
Versatility: Ideal for multiple applications such as backup power systems, solar installations, and vehicles.
Longevity: Their sealed construction provides a longer shelf life and improved durability compared to traditional flooded lead-acid batteries.

Low Maintenance: VRLA batteries require little to no maintenance, making them convenient for long-term use.

Overall, VRLA batteries are a reliable and efficient choice for diverse energy storage needs due to their safety, versatility, and long-lasting performance.

Limitations of VRLA Batteries

Higher Initial Cost: VRLA batteries are generally more expensive than traditional flooded lead-acid batteries.

Temperature Sensitivity: Their performance and lifespan decrease significantly in high-temperature environments.
Limited Deep Discharge Capability: Frequent deep discharges can reduce the overall life of the battery.
Difficult to Repair: The sealed design makes them non-serviceable and difficult to repair once damaged.

Charging Sensitivity: They require precise charging control to prevent overcharging, which can lead to drying out or reduced efficiency.
Lower Energy Density: Compared to newer technologies like lithium-ion batteries, VRLA batteries store less energy per unit weight.

In summary, while VRLA batteries are safe and maintenance-free, their cost, temperature sensitivity, and limited deep discharge tolerance make them less suitable for some demanding applications.

Applications of Valve Regulated Lead Acid (VRLA) Batteries

Telecommunication Systems: Used for backup power in telephone exchanges, data centers, and communication towers.
Uninterruptible Power Supply (UPS): Provides instant backup power during mains failure to protect sensitive equipment.
Renewable Energy Systems: Commonly used in solar and wind energy storage setups due to low maintenance and reliability.

Emergency Lighting: Powers emergency lighting systems in buildings, hospitals, and industrial facilities.
Automotive and Electric Vehicles: Used in start-stop systems, hybrid vehicles, and auxiliary power applications.
Power Plants and Substations: Supports control systems and protection relays during power interruptions.

Security and Alarm Systems: Ensures continuous operation of surveillance, alarm, and access control systems.
Portable and Medical Equipment: Supplies power to portable devices and critical medical instruments during outages.
Railway and Aviation: Provides backup for signaling, control, and navigation systems.

Conclusion

Valve Regulated Lead Acid (VRLA) batteries are an advanced form of lead-acid batteries designed for safety, reliability, and maintenance-free operation. Their sealed and spill-proof design allows flexible installation and makes them ideal for use in UPS systems, telecom setups, renewable energy storage, and emergency power applications.

While VRLA batteries offer several benefits such as long life, low maintenance, and high efficiency, they also have limitations like higher cost and temperature sensitivity. Overall, VRLA batteries remain one of the most trusted and widely used energy storage solutions for both industrial and commercial applications.

VRLA Battery | Working, Benefits , Limitations and applications

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