What is VRLA Battery : Construction & Its Working

To know with the detailed concept of VRLA battery, let us start by knowing its history. So, the first lead acid-based gel battery was introduced by Fabrik Sonneberg in the year 1934 and the modernized type of this battery was designed by Otto in the year 1957. And the first cell which was developed using this technology was Cyclon. Then after with the development of technologies and trends, in the mid-period of the 1980s UK industries Tungstone developed AGM batteries that have a life period of 10 years. And let us have a clear discussion on the VRLA battery, its working, construction, and related concepts.

What is a VRLA Battery?

Definition: VRLA is the valve-regulated lead-acid battery which is also termed as a sealed lead acid battery that comes under the classification of the lead-acid battery. This is considered through a specific quantity of electrolyte which gets absorbed in a plate extractor or it will develop into a gel-like consistency thus balancing both the positive and negative plates. Because of this recombination of oxygen happens in the cell and the existence of the relief valve which keeps up battery fillings that self- regulates the battery cell positions.

VRLA Construction

The construction of a VRLA battery can be explained as follows:

The cells in the battery are constructed of flat plates that are identical to the standard lead-acid battery cells or they might be constructed either in a spiral roll type also. These batteries consist of a strain relief valve where it gets activated when the battery initiates to build hydrogen gas pressure which means that it gets recharged. The activation of this valve permits some of the gas quantity to get escaped so that the entire battery capacity will get lessened.

VRLA Battery Construction
VRLA Battery Construction

Or else the cells which are in rectangle shape also have valves that are inserted to function at either 1 (or) 2 psi coils of spiral cells having outside containers. There exist vapor diffusers for the cell covers which are used for safe dispersion of additional hydrogen gas which is formed at the time of overcharging. There will be no permanent protection for these but are managed to be free from maintenance.

This kind of batteries can be aligned in any direction, in contrast to the general lead batteries because they have to be kept in the upright direction to prevent any kind of acid spillover and also to look over if there happens any vertical alignment of the plates. Because when compared with vertical alignment, horizontal alignment enhances the life period.


When operated at extreme over range current values, then there happens water electrolysis thus ejecting H2 and O2 gases via battery valves. At this time, there has to be additional maintenance to avoid any kind of prompt charging or short circuits. Even any other technologies are used, there will be persistent voltage charge, enhanced efficiency, and quick charge for the VRLA battery.

VRLA batteries might be persistently float charged nearly across 2.18-2.27 volts per each cell at a temperature of 25 °C, based on the specifications mentioned by the battery manufacturer.

VRLA Battery Working

The basic working principle of VRLA battery can be explained as follows:

As lead acid kind of batteries is included with lead plates serving as electrodes, immersed in the electrolyte that has liquid kind of sulphuric acid. In the same way, the VRLA battery also has a similar kind of chemistry, and the electrolyte in this kind of battery is immobilized.

In AGM (Absorbed Gel Matt) type of VRLA battery, the electrolyte is in fiberglass matt type, whereas in gel kind of batteries, it is in the form of a paste. At the time of cell discharge, diluted acid and the lead in the battery goes through some chemical reaction where it delivers water and lead sulfate. And when the discharge process is continued, the water and lead sulfate are again formed into acid and lead.

In the entire lead-acid type of batteries, the charging current has to be in synchronization with the battery ability so that the energy gets absorbed. When the value of the charging current is more, then the electrolysis process takes place which decomposes water as O2 and H2. When both these gases are escaped, then there has to be continual addition of water into the battery.

While in VRLA battery, they preserve the generated gases internal to the battery till the time that pressure levels are in a safe limit.  In general functioning scenarios, the gases might get combined inside the battery or in some cases using a catalyst substance or an electrolyte. Though the pressure value surpasses the safety levels, then safety valves are opened to allow additional gases to escape. And thus because the pressure is regulated to the permitted levels. Because of this, the batteries are named as “Valve Regulated”.

VRLA Life Cycle Calculation

In the VRLA battery life cycle, the battery undergoes deep discharge when the primary power sources that are used are solar, golf carts, and others. Then the battery gets again recharged thus following the discharge to get back to its ability so that it is used again and again. Whereas in a conventional cycle, the cycle gets repeated again.

This causes increased stress on the positive plate where it causes the paste to drop from the grid section. So, for these kinds of applications, there is a technology termed as a deep cycle service. This is developed by AGM battery which is designed specially to deliver enhanced life cycles for a regular cycle and deep applications. In order to enhance the cycle life, this technology is included with a positive paste type of formula.

This is done because to address pressure which is developed at the time of structural modifications those happen in the charge or discharge cycle. So, the amalgamation of both the grid and positive paste allows the extendibility, and this increases the life cycle service.

Like this, the VRLA battery life cycle is calculated.

Testing Procedure

The VRLA battery testing procedure should be done only in the temperature ranges of 650F to 900F.

Few of the prerequisites to be taken care before testing are:

  • The equalized charge should be finished within 3 days at the condition of 2.40 vpc
  • A floating value of not minimal to 72 hours needs to sync up with the equalized charge to initiate the test. The entire battery voltages are supposed to be in the limit of tolerance values.

The discharge timings should be 1 to 8 hours maintained at an end cell voltage value of nearly 1.75 Vpc.

A few of the points those are to be recorded at the time of test are:

  • Before the testing procedure, record each floating voltage level of the system.
  • Also, record the floating voltage level at the battery edges
  • Record the floating voltage value of every section before the test procedure
  • Make sure to note down both the ambient temperature levels along with battery temperature values at the negative edge
  • At the time of periodic time intervals, calculate entire DC voltage, DC amps ad each cell voltage levels
  • As the testing procedure reaches the end, readings have to be calculated more regularly to look at the cells that reach lesser voltage values.

VRLA Applications

The applications of VRLA battery are:

  • Modern-day automobiles employ AGM type of VRLA batteries to lessen the probability of acid spillover.
  • Implemented in luxurious automobiles
  • Used in stability maintenance and in navigation
  • Used in the applications to deliver enhanced electrical dependability than that of lead-acid batteries
  • Implemented in computer control to make sure that alternator modifies the battery at the time of car deceleration
  • Used in ice monitoring network in the remote sensors
  • VRLA batteries are employed specifically in the power wheelchairs and in UPS

Apart from this, there exist multiple VRLA advantages and disadvantages. Based on the manufacturer and specifications, they differ in every source. And this is all about the concept of VRLA battery. This article has provided a complete description of VRLA battery, working, design, benefits, testing, and uses. Also, crucial to know what is the difference between vrla and smf battery?