VRLA Battery, Working, Types, Maintenance, Application

A VRLA battery, which stands for Valve-Regulated Lead-Acid battery, is a type of sealed lead-acid battery that incorporates a specific amount of electrolyte, either absorbed in a plate separator or immobilized in a gel-like substance. These batteries are commonly referred to as sealed lead-acid batteries due to their construction, which prevents the escape of electrolyte. The term “valve-regulated” indicates the presence of a safety valve that regulates the internal pressure of the battery, thereby averting electrolyte evaporation and reducing the risk of explosion.

The primary advantage of VRLA batteries lies in their maintenance-free operation, making them highly suitable for various applications. They are frequently utilized in uninterruptible power supply (UPS) systems, emergency lighting installations, and telecommunication equipment where continuous and hassle-free functionality is imperative. Additionally, VRLA batteries find extensive application in electric vehicles, renewable energy systems, and other contexts that necessitate a reliable and secure energy storage solution.

VRLA batteries can be classified into two main types: Absorbed Glass Mat (AGM) and Gel batteries. AGM batteries employ a glass mat separator to absorb the electrolyte, while gel batteries utilize a silica gel to immobilize the electrolyte within the battery. Both AGM and gel VRLA batteries are engineered to be maintenance-free and possess an extended service life, offering versatility and durability for various applications.

VRLA battery Working Principle:

Designs of the batteries are a little different from the general lead-acid battery because no valves are present in these batteries to eject O2 Gas. It is designed in a way that the negative plate will not fully charge even when positive plates are in full charge condition. Here, no H2 gas generates from the negative plates and O2 gas generates from the overcharged positive plates.

Step1: The generated O2 gas from the positive plates reacts with charge spongy leads(Pb) of negative plates and generate Lead Monoxide(PbO).

Pb + ½ O2       →   PbO

 Step-2: The generated Lead Monoxide again reacts with the Sulfuric Acid (H2SO4) in the electrolyte and generates Lead Sulphate (PbSO4).

PbO  +  H2SO4  →  PbSO4  +  H2O

Step-3: The generated Lead Sulphate (PbSO4) again reform and generates Sulfuric Acid and Lead(Pb).

PbSO4 + 2e- + 2H+   →  H2SO4  +  Pb

This process prevents to loss of water. In this way, O2 generates from the overcharged positive plates automatically absorbed by the negative plates and ejection of O2 not require. No initial charging is required for this battery.


Ther are two types of VRLA battery present.

  1. Absorbent Glass Mat (AGM)
  2. Gel cell
  • Absorbent Glass Mat (AGM)

 In this battery, a thin ultra-fine fiberglass mat placed between the plates of electrodes. The fiberglass mats easily absorb the electrolyte and do not affect by the electrolyte. This mat packs in between the plates and slightly compressed and fix at the place. These batteries are vibration-proof because of using of glass mat and tightly packing inside the battery.

It has low internal resistance and charging and discharging capacity is very fast. The service life of the battery is very long and it is very much safer to use. This battery uses in the vehicles, UPS and other power storage devices.

2. Gel Cell Battery:

In this battery, the electrolyte used in gel form. The sulfuric acid is mixed with fumed silica and which makes the resulting mass gel and immobile. Gel batteries are robust and versatile.

Gel cell batteries can make in small size and ratings which are used in various small electronics devices. These batteries are also used in emergency light, UPS system, storage of solar power and other home and office backup power system.

Specification of VRLA Battery:

The specifications of a VRLA (Valve-Regulated Lead-Acid) battery can vary depending on the particular model and intended application. However, here are some commonly encountered specifications associated with VRLA batteries:

  1. Voltage: VRLA batteries are available in a range of voltage ratings, such as 6V, 12V, 24V, or higher, depending on the specific requirements of the application.
  2. Capacity: The capacity of a VRLA battery refers to its ability to store electrical charge and is typically specified in ampere-hours (Ah) or milliampere-hours (mAh). Higher capacity batteries have the capability to store more energy and provide prolonged backup power.
  3. Physical Dimensions: VRLA batteries come in various sizes and shapes to accommodate different applications. The physical dimensions are typically described in terms of length, width, and height. Standard form factors like Group 24, Group 31, or other similar sizes are commonly available from different battery manufacturers.
  4. Weight: The weight of a VRLA battery is an important factor, particularly in applications where portability or weight limitations are a concern. The weight is typically indicated in kilograms (kg) or pounds (lb).
  5. Design Life: VRLA batteries have a predetermined design life, which denotes the expected duration of service under normal operating conditions. The design life is usually specified in terms of the number of years or cycles the battery can endure before experiencing a decline in performance.
  6. Terminal Type: VRLA batteries are equipped with specific terminal types to facilitate easy connection and compatibility with the intended equipment. Common terminal types include threaded terminals, bolt terminals, or a combination thereof.
  7. Self-Discharge Rate: VRLA batteries exhibit a self-discharge rate, indicating the rate at which the battery gradually loses its charge when not in use. Lower self-discharge rates imply longer shelf life and extended storage periods without the need for frequent recharging.
  8. Operating Temperature Range: VRLA batteries are designed to operate within specific temperature ranges to ensure optimal performance. The operating temperature range is typically specified as a minimum and maximum temperature, enabling the battery to function reliably in diverse environmental conditions.

Maintenance of VRLA Battery

However, the VRLA battery is called maintenance-free, following maintenance procedures follow for increasing the life of the battery.

  1. Cleaning and tightness of battery terminals
  2. Remove dust from the batteries and clean the battery box to avoid rusting.
  3. Maintain the Temperature of the battery room. It is very much sensitive to temperature. Always maintain the room temperature at 20-24 degrees centigrade as recommended by the manufacturer.
  4. During long storage, scheduled charging and discharging of the battery is also important to increase the life of battery.
  5. Including the above also follow the manufacturer-specific guidelines or manual for maintenance.

VRLA Battery Charging Procedure.

Proper charging of the battery is important for the healthiness of the battery. Always charge the VRLA battery with the specific charger as per the voltage and current rating of the battery. Float mode (low charging current) and boost mode (High charging current) are available in the charger.

Procedures for charging of VRLA battery (cell voltage-2V) are below.

  1. Check the individual cell voltage and if the voltage is above 2V, select the charger in float mode.
  2. Set charging voltage at 2.25 V per cell, example, for 100 nos. of cells battery total charging voltage will be (100X2.25)=225V
  3. If the voltage falling below 2.2V, then select the charger in boost mode.
  4. Set charging voltage at 2.3V per cell, for example for 100 nos. of cells battery total charging voltage will be (100X2.3)=230V.
  5. Avoid overvoltage during charging. Charging voltage must not increase above 2.35V.
  6. Always follow the instruction manual for using the float and boost mode for charging of the battery.

Advantages of VRLA Battery:

VRLA (Valve-Regulated Lead-Acid) batteries offer numerous advantages that contribute to their widespread use in various applications. Here are some key advantages associated with VRLA batteries:

  1. Maintenance-Free Operation: A notable advantage of VRLA batteries is their maintenance-free nature. Unlike traditional lead-acid batteries, VRLA batteries do not require regular electrolyte refilling or watering. This characteristic simplifies their use and eliminates the need for frequent maintenance, saving time and effort.
  2. Sealed Construction: VRLA batteries are designed with a sealed construction, ensuring that they remain sealed during normal operation. This sealed design eliminates the need for venting and offers multiple benefits. It reduces the risk of electrolyte leakage, enhances safety by preventing exposure to hazardous materials, and enables the battery to be used in different orientations (such as lying on its side).
  3. Enhanced Safety: The valve-regulated design of VRLA batteries incorporates a safety valve that regulates internal pressure. This valve prevents the accumulation of excessive pressure within the battery, minimizing the risks of explosion or electrolyte evaporation. Consequently, VRLA batteries are considered safer and more stable compared to traditional vented lead-acid batteries.
  4. Versatile Applications: VRLA batteries find applications in a wide range of industries and systems. They are commonly used in uninterruptible power supply (UPS) systems, emergency lighting, telecommunications equipment, electric vehicles, renewable energy systems, and more. The ability of VRLA batteries to deliver reliable and consistent power makes them suitable for various critical and backup power applications.
  5. Long Service Life: VRLA batteries are designed to have a long service life, providing reliable performance over an extended period. With proper maintenance and appropriate charging practices, VRLA batteries can deliver consistent performance and meet the demands of different applications.
  6. Improved Efficiency: VRLA batteries exhibit relatively high energy density, allowing them to store a significant amount of energy in a compact size. This high energy density translates into improved efficiency in terms of power delivery, making VRLA batteries an efficient choice for demanding applications.
  7. Environmental Friendliness: VRLA batteries are generally regarded as more environmentally friendly compared to other battery types. Their sealed construction helps prevent the release of hazardous substances into the environment. Additionally, many VRLA batteries are designed with recyclable materials, making them easier to dispose of or recycle at the end of their service life.

These advantages make VRLA batteries a preferred choice in various applications where reliable, maintenance-free operation, enhanced safety, and versatility are crucial considerations.


VRLA (Valve-Regulated Lead-Acid) batteries have various applications due to their many advantages. Here are some common uses of VRLA batteries:

  1. Backup Power: VRLA batteries are commonly used in UPS (Uninterruptible Power Supply) systems to provide backup power during mains electricity outages. They keep critical equipment like computers, servers, and communication systems running smoothly.
  2. Emergency Lighting: VRLA batteries are used in emergency lighting systems, such as exit signs and backup lights. They ensure that emergency lighting remains operational during power failures or evacuation situations.
  3. Telecommunications: VRLA batteries play a crucial role in maintaining reliable power for telecommunication equipment like mobile phone base stations and communication towers. They provide uninterrupted power to keep communication services operational.
  4. Electric Vehicles (EVs): VRLA batteries are utilized in electric vehicles like cars, buses, and motorcycles. They store electrical energy to power the vehicle’s motor, offering clean and efficient transportation options.
  5. Renewable Energy Systems: VRLA batteries are used in renewable energy systems, such as solar power and wind power installations. They store excess energy generated during peak production and release it when there is low or no production, ensuring a steady power supply.
  6. Marine Applications: VRLA batteries are suitable for marine applications, including boats and yachts. They provide reliable power for auxiliary systems, navigation equipment, lighting, and engine starting.
  7. Medical Equipment: VRLA batteries are used in medical equipment and devices that require a stable and uninterrupted power source, such as patient monitoring systems and portable medical devices.
  8. Security Systems: VRLA batteries are employed in security systems like burglar alarms and surveillance cameras. They ensure continuous power supply, even during power disruptions or outages.
  9. Portable Power: VRLA batteries are utilized in portable power solutions, such as camping equipment, portable lighting, and off-grid power systems. They provide reliable and portable energy storage for various outdoor and remote applications.

VRLA vs lithium-ion battery

VRLA BatteryLithium Battery
High Power to weight ratioLow power to weight ratio
The efficiency of discharge rate is highThe efficiency of discharge rate is low
Fast charging capacityLow charging capacity
wide usable temperature rangeUse only lower temperature around 20-24 degree celsius
High manufacturing costLow manufacturing cost
Life is about 4 to 5 yearsLife is about 10-15 years
Very small size and rating are availableCompare to higher size and rating available
To summarise, VRLA batteries, also known as sealed lead-acid batteries, are sealed batteries that use a specific amount of electrolyte and incorporate a safety valve for pressure regulation. These batteries are widely used in applications that require maintenance-free operation, such as UPS systems and emergency lighting. They are available in AGM and gel types, both of which provide long-lasting performance and reliability to meet diverse energy storage needs.

Leave a Comment