VRLA battery
[4] Due to their construction, the gel cell and AGM types of VRLA can be mounted in any orientation and do not require constant maintenance.
They are widely used in large portable electrical devices, off-grid power systems (including uninterruptible power systems), low-cost electric vehicles, and similar roles, where large amounts of storage are needed at a lower cost than other low-maintenance technologies like lithium ion.
Varley adapted the Cyclon lead foil technology to produce flat-plate batteries with exceptional high rate output.
[12] The cell covers typically have gas diffusers built into them, which allow safe dispersal of any excess hydrogen that may be formed during overcharge.
Very thin glass fibers are woven into a mat to increase the surface area enough to hold a sufficient amount of electrolyte on the cells for their lifetime.
Originally a kind of gel battery was produced in the early 1930s for portable valve (tube) radio LT supply (2, 4, or 6 V) by adding silica to the sulfuric acid.
Earlier "wet" cells in glass jars used special valves to allow tilt from vertical to one horizontal direction, in 1927 to 1931 or 1932.
Chemically, they are almost the same as wet (non-sealed) batteries except that the antimony in the lead plates is replaced by calcium, and gas recombination can take place.
Many modern motorcycles and all-terrain vehicles (ATVs) on the market use AGM batteries to reduce the likelihood of acid spilling during cornering, vibration, or after accidents, and for packaging reasons.
AGM batteries are also commonly used in classic vehicles, since they are much less likely to leak electrolyte, which could damage hard-to-replace body panels.
VRLA batteries are used extensively in power wheelchairs and mobility scooters, as the extremely low gas and acid output makes them much safer for indoor use.
VRLA batteries are also the standard power source in sailplanes, due to their ability to withstand a variety of flight attitudes and a relatively large ambient temperature range with no adverse effects.
[19] VRLA batteries are used in the US Nuclear Submarine fleet, due to their power density, elimination of gassing, reduced maintenance, and enhanced safety.
They typically are favored for their low-maintenance and spillproof qualities, although they are generally considered a less cost-effective solution relative to traditional flooded cells.
In telecommunications applications, VRLA batteries that comply with criteria in Telcordia Technologies requirements document GR-4228, Valve-Regulated Lead-Acid (VRLA) Battery String Certification Levels Based on Requirements for Safety and Performance, are recommended for deployment in the Outside Plant (OSP) at locations such as Controlled Environmental Vaults (CEVs), Electronic Equipment Enclosures (EEEs), and huts, and in uncontrolled structures such as cabinets.
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 fumes are emitted during normal operation.
Flooded-cell gas emissions are of little consequence in all but the smallest confined areas and pose very little threat to a domestic user, so a wet-cell battery designed for longevity gives lower costs per kWh.
There is no need (or ability) to check the level of electrolyte or to top up water lost due to electrolysis, thus reducing inspection and maintenance requirements.
When the absorption stage voltage setpoint is reached (and charge current has tapered off), the charger switches to a float voltage setpoint at a very low C-rate to maintain the battery's fully charged state indefinitely (the float stage offsets the battery's normal self-discharge over time).
