
vrla batteries and flooded lead-acid batteries
Compared with flooded lead-acid batteries, VRLA batteries offer several advantages. The battery can be mounted in any position, since the valves only operate on over pressure faults. Since the battery system is designed to be recombinant and eliminate the emission of gases on overcharge, room ventilation requirements are reduced and no acid fume is emitted during normal operation. The volume of free electrolyte that could be released on damage to the case or venting is very small. There is no need (nor possibility) to check the level of electrolyte or to top up water lost due to electrolysis, reducing inspection and maintenance.
These batteries are often colloquially called sealed lead-acid batteries, but this term is misleading: a sealed battery would be a safety hazard due to overpressure risks when overcharging, and there is always a safety valve present, hence the name valve-regulated. Sealed is opposed to vented (also called flooded). Because VRLA batteries use much less electrolyte (battery acid) than traditional lead-acid batteries, they are also occasionally referred to as an "acid-starved" design.
The name "valve regulated" does not wholly describe the technology; these are really "recombinant" batteries, which means that the oxygen evolved at the positive plates will largely recombine with the hydrogen ready to evolve on the negative plates, creating water—thus preventing water loss. The valve is strictly a safety feature in case the rate of hydrogen evolution becomes dangerously high.
One result of this design is a much higher ratio of power to "floorspace" than large, flooded type battery systems; another is a high-rate power capacity, though of relatively short duration. As a result, VRLA batteries are frequently employed in UPS (uninterruptible power supply) or other high-rate applications. Long duration applications such as telecommunications are not as well-suited to VRLA batteries, as there are other, more applicable battery designs available.[


