Valve Regulated Lead Acid Batteries
Valve regulated lead acid (VRLA) batteries are also called sealed lead acid (SLA) batteries. Please don’t mix with SLI batteries, which are starting, lighting and ignition batteries. Of course, these lead acid batteries also uses sulfuric acid electrolyte which produce a chemical reaction when discharged and charged.
This construction is designed to prevent electrolyte loss through evaporation, spillage and gassing and this in turn prolongs the life of the battery and eases maintenance. Instead of simple vent caps on the cells to let gas escape, VRLA have pressure valves that open only under extreme conditions. Valve-regulated batteries also need an electrolyte design that reduces gassing by impeding the release to the atmosphere of the oxygen and hydrogen generated by the galvanic action of the battery during charging. This usually involves a catalyst that causes the hydrogen and oxygen to recombine into water and is called a recombinant system. Because spillage of the acid electrolyte is eliminated the batteries are also safer.
VRLA-AGM batteries indicate valve-regulated lead acid batteries with absorbed glass mat (AGM) separators. A VRLA-AGM battery uses recombinant technology. The oxygen produced from the positive plates of the battery is absorbed by the negative plates. This suppresses the generation of hydrogen at the negative plates. The recombination of oxygen and hydrogen leads to water, retaining the electrolyte amount within the battery. Water filling is never required. Battery should never be opened as this would damage the battery with additional oxygen from the air. The warranty will be void if the battery is opened.
Lead acid batteries are cheap and can store large amounts of energy. But if they are repeatedly and rapidly charged and discharged – as happens when storing braking energy from an HYBRID-electric vehicles (HEV) and then releasing it when it accelerates – the battery’s negative plate becomes coated with deposits. That limits its working life to a few years and is one reason why today’s HEVs, such as the Toyota Prius, use NiMH batteries.
Source: www.leoch.com
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