Valve Regulated Lead Acid (VRLA) Batteries are low maintenance sealed lead-acid batteries. They limit inflow and outflow of gas to the cell – thus the term “valve regulated”. VRLA batteries are unique due to the fact that they contain a “starved” electrolyte (acid), which is absorbed or immobilized in a separator.
Electrolytes are commonly absorbed or immobilized in two ways:
Absorbed electrolyte: a highly porous mat made from microglass fibers is partially filled with electrolyte, acting as a separator. Also called AGM for Absorbed Glass Mat.
Gelled electrolyte: Fumed silica is hardened into a gel that free-floats in its container. During charges, the gel dries more creating cracks and fissures develop between the positive and negative. Often referred to as Gel Cell.
· Moderate Life
· High-rate capacity
· High charge efficiency
· No “memory effect”
· State of charge can be determined by measuring voltage
· Relatively low cost
· Available in a variety of sizes and voltages from single cell units (2V) to 48V or higher
· Cannot be stored in discharged condition
· Relatively low-energy density
· Lower cycle than NiCad batteries
· Thermal runaway can occur with incorrect charging or improper thermal management
· More sensitive to temperatures than conventional lead-acid batteries
According to BatteryUniversity.com, “heat reduces the life of VRLA. Most batteries are enclosed in spaces without proper ventilation or cooling. Every 8°C (15°F) rise in temperature cuts the battery life in half. A VRLA battery, which would last for 10 years at 25°C (77°F), will only be good for 5 years if operated at 33°C (95°F). Once damaged by heat, no remedy exists to improve capacity.”
· Always store in a charged condition. Never allow the open cell voltage to drop below 2.10V. Apply a topping charge every six months or when recommended.
· Avoid repeated deep discharges. Charge more often.
· Prevent sulfation and grid corrosion by choosing the correct charge and float voltages. If possible, allow a fully saturated charge of 14h.
· To reverse sulfation, raise the charge voltage above 2.4V per cell for a few hours.
· Avoid operating lead-acid at elevated ambient temperatures.
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