VRLA batteries are maintenance free batteries. VRLA stands for Valve Regulated Lead Acid is the technical term for maintenance free batteries. VRLA batteries are also popularly called Sealed Maintenance Free batteries or SMF batteries in short.

VRLA batteries work on the oxygen recombination principle. The hydrogen and oxygen that are emitted in flooded lead acid batteries recombine in VRLA batteries to form water. That is why you don’t have to add distilled water from outside as in the case of FLA batteries, which is what makes them maintenance free.

However, the recombination process is not 100% efficient. So over time, the released gases that have not recombined collect inside the VRLA batteries thus increasing the internal pressure, and have to be released to maintain the optimum pressure. This is achieved with the help of one-way, pressure-sensitive valves which open when the internal pressure increases above a certain threshold and allow the excess gases to be vented. That is why these batteries are called VRLA or valve regulated lead acid batteries. Excess gases are also produced if these batteries are overcharged or discharged at rates higher than the recommended rate.

The main advantages of VRLA batteries compared to flooded lead acid batteries are:

  • They do not produce gases during normal operation or while charging and can therefore be kept in the vicinity of any electrical equipment or any inflammable material, unlike FLA batteries.
  • They do not emit acid spray even if charged abusively. However, charging abusively will impact the battery life adverselyand should be avoided at all costs.
  • They are spill-proof and leak-proof.
  • They can be used in horizontal position also which is something that you cannot do with FLA batteries.
  • They can be transported without any restrictions:
    • Surface transport: Classified as non-hazardous material as per DOT-CFR Title 49 parts 171-189.
    • Marine transport: Classified as non-hazardous material as per IMDG amendment 27.
    • Air transport: Comply with IATA/ICAO, Special Provision A67.

The main disadvantages of VRLA batteries compared to flooded lead acid batteries are:

  • They provide lesser discharge currents compared to FLA batteries.
They are more expensive compared to FLA batteries.