A VRLA battery is short for “valve-regulated lead-acid battery.” It is also called sealed battery or a maintenance free battery.
This battery is used for power applications that traditionally relied on vented or wet lead acid cells. These include off-grid power systems, portable electrical devices and other applications that require affordable large-scale power storage.
There are two primary types of VRLA batteries: the AGM (absorbed glass mat) and Gel cells. Both of these VRLA types have the same container, plates and pressure relief valves.
In an AGM VRLA battery, the electrolyte is inside a glass mat and not flooding the plates freely. The very thin glass fibers are woven into a mat to maximize the surface area to hold sufficient electrolytes to last throughout the battery’s life. The separator is not immersed in the electrolyte completely, so that the 2%-10% space will allow the oxygen recombination cycle to occur.
The Deep Cycle Service (DCS) AGM provides the longest life for services that are frequent and deep. The battery contains a positive paste formula that allows it to address the stress that happens during frequent discharge/charge cycle. It is combined with a grid alloy that lessens the grid corrosion.
The MR (Modular Range) valve regulated AGM has absorbent separators. The separator is made of a non-woven material that allows the plates to be fully wet by the electrolytes. It also permits the oxygen generated to pass freely during charging.
The Gel VRLA battery or gel cell has an electrolyte that is gelified. That means the sulfuric acid is combined with fumed silica. It reduces the evaporation, spilling and corrosion problems that are common to wet-cell batteries. It allows the battery to withstand extreme temperatures, vibration and shock. The gel has cracks in it to allow oxygen to travel from the positive to the negative plate – thus permitting the oxygen recombination cycle to happen.
The VRLA battery is also used in UPS and Telecom applications to allow important infrastructures to function during a power outage.
Here are the important characteristics of both types of VRLA batteries (see also Gel vs. AGM):
- Battery capacity and performance. The AGM has more electrolytes because the gelling agent displaces the electrolytes. This give the battery 7%-8% more duration capacity. The AGM also has a lower internal drop that allows a longer run despite a high discharge rate.
- Elevated temperature. The AGM battery is more efficient in the oxygen recombination cycle that allows it to draw 50% more float current. But the Gel cell is 15% more efficient in heat conduction because the gelled electrolytes are in complete contact with the plates and walls of the container.
- Float service life. Both the AGM and Gel VRLA batteries have the same 95%-100% capacity.
The following table describes the different VRLA types and their respective applications.
It is important to use the right battery for the specific application to maximize the power density, high rate performance and life of the battery.
Related Articles:
Valve Regulated Lead Acid (VRLA) Batteries
2 Comments
i ordered a 12 volt blue battery for a power wheel tractor and got a SLA VRLA battery along with the 12 volt blue. what is the VRLA for and how do you charge it i bought it from ebay.
VRLA is valve regulated sealed lead acid, the full name of the battery chemistry. You can charge it with the same charger as you’ve been using. The previous battery was the same, even though it may not have been labeled VRLA.