What are Valve Regulated Lead Acid (VRLA) Batteries?

These batteries are popularly termed as maintenance free lead-acid batteries. Each cell in VRLA battery will have a value (automating operating) to allow the gas to escape if developed by the overcharging the cells and to hinder the entrance of oxygen from the air into the cell.

Fig. Valve Regulated Lead Acid Battery

These VRLA batteries are also called sealed lead acid batteries and also recombinant batteries. Oxygen which evolves during discharging at the positive plate of the battery recombine with the hydrogen which evolves at the negative plate of the cell to form water. This results in prevention of the water loss and unlike flooded batteries water is not needed to be added periodically. The valve present in VRLA cell acts as a safety valve which opens when the concentration of hydrogen gas inside the battery increases dangerously high.

Valve-Regulated LA (VRLA) has become a popular battery for powering Electric Vehicles because of its high specific power, low initial cost, and quick charge capability, and no maintenance requirement.

Common VRLA batteries include adsorbed glass material (AGM) and GEL batteries.

AGM batteries are composed of electrolyte made of fiberglass, which is a solid material, to absorb and contain acid without leakage. These types of batteries have a compact volume and occupy minimal space such that vibration resistance is higher than that of standard batteries. The special feature of this battery type is that it recombines hydrogen and oxygen into the loss of water.

GEL batteries are manufactured with gel state electrolyte, which is a gelatinous mass that is not fully solid to contain acid and has no leakage.

GEL batteries need slower and controlled charging compared with other batteries. However, gas bubbles could be produced inside the gel electrolyte, which could damage the battery permanently.

Advantages of Valve Regulated Lead Acid Battery

  1. VRLA battery is maintenance free and no periodic water refilling is not required.
  2. Reduced demand on ventilation.
  3. The capacity range of VRLA battery is high (12000 Ah).
  4. VRLA batteries will have a longer life. The lifespan of this batteries will be around 10 years.
  5. Feasibility for float charge operation with the same voltage of the cells, to continue in using existing charging equipment.
  6. VRLA batteries are economical.

Applications of Valve Regulated Lead Acid (VRLA) Battery

  1. UPS
  2. Emergency Lights
  3. Electric Vehicles
  4. Renewable Energy


Question: What factors that decide the VRLA battery to completely charged from the fully discharged condition?

Answer. Some of the important factors that determine the duration of the discharged battery to charge are:

  1. Duration of the discharge occurred
  2. Temperature at which battery is operating
  3. Size and efficiency of the charger

Question: Can VRLA batteries be enclosed in sealed containers?

Answer. VRLA batteries should not be enclosed in the sealed containers. Oxygen and hydrogen gases are produced in the battery, however, they once again convert back to water. But during overcharging these gases escape out of the cell. If the batteries are enclosed inside a sealed container, the pressure inside the container due to hydrogen and oxygen increases and may explode.


image reference: motolite.com

Valve Regulated Lead Acid (VRLA) Batteries | Advantages

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