Valve Regulated Lead Acid Batteries (VRLA) are also known as Sealed Lead Acid Batteries. Unlike flooded lead acid batteries where the electrolyte is a liquid, VRLA batteries use either:
- absorbent glass mats impregnated with electrolyte (see AGM batteries)
- or a silicon based gel electrolyte (see Gel batteries).
With no liquid to top off the batteries, they can be sealed. Which allows them to operate at any angle without the risk of leaks. However, it is still possible for such a battery to malfunction or to be abused (such as through overcharging) which can lead to heat and gas build up internally. To ensure that this does not lead to an explosion the batteries have valves which allow gases under pressure to escape – hence the term ‘Valve Regulated’.
The sealed nature of VRLA batteries means many are termed ‘maintenance free’ but as this also sometimes appears on flooded lead acid batteries it should not be assumed all maintenance free products are VRLA.
See What is a lead acid battery for more detail on the two types of VRLA and a comparison with flooded lead acid.
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