VRLA Battery – Everything You Need to Know About
A Complete Guide to VRLA Batteria – The Valve-Regulated Acido di piombo Battery Technology
1. What Does VRLA Mean?
VRLA stands for Valve-Regulated Lead-Acid batteria. It is a sealed type of lead-acid battery that uses a pressure-regulating valve system to control internal gas buildup.
Key features:
Sealed construction: The electrolyte is immobilized—either absorbed in a glass fiber separator (AGM type) or suspended in a silica-based gel (GEL type).
Valve control: A pressure-sensitive safety valve on top opens to release excess gas (oxygen and hydrogen) during overpressure conditions, preventing an explosion.
Oxygen recombination cycle: Oxygen produced at the positive plate migrates to the negative plate and reacts with lead to form water, maintaining electrolyte balance without water loss.
This design makes VRLA batteries Senza manutenzione E spill-proof, con no need to add water during their service life.
2. VRLA Battery Technology: A Brief History
Before the 1970s, lead-acid batteries required the plates to be submerged in free-flowing sulfuric acid, which led to water loss during charging due to electrolysis.
Key milestones in VRLA technology:
| Year | Innovation |
|---|---|
| 1957 | German company Sonnenschein developed the SiO₂ gel-sealed lead-acid battery, pioneering the GEL VRLA format. |
| 1971 | Gates Energy, USA, introduced AGM (Absorbent Glass Mat) separators, solving the oxygen recombination problem and improving gas control. |
| 1973 | Small-size VRLA batteries became commercially available, opening the door to UPS systems, telecom backup, E wheelchair power applications. |
Oxygen Recombination Reaction:
During charging, oxygen is generated at the positive plate:
This oxygen diffuses to the negative plate, where it recombines into water, eliminating the need to refill water and ensuring internal pressure control.
Side Reactions:
Despite the recombination mechanism, two side reactions still occur:
Hydrogen evolution (at negative plate):
2H⁺ + 2e⁻ → H₂Grid corrosion (at positive plate):
Pb + H₂O → PbO₂ + 4H⁺ + 4e⁻
To suppress these, manufacturers use lead-calcium alloy plates, which significantly reduce hydrogen evolution and improve battery life.
3. How Does a VRLA Battery Work?
Here’s a simplified schematic diagram of the VRLA battery’s internal working mechanism:
Key elements in the operation:
The safety valve regulates internal gas pressure.
O₂ and H₂ are managed through an internal recombination system.
AGM or GEL holds the electrolyte in place.
Electrochemical reactions are designed to recycle water internally, making the system sealed and low-maintenance.
4. Pros and Cons of VRLA Battery
Comparison with Other Battery Technologies
| Category | VRLA Battery | Flooded Lead-Acid | Lithium-ion | NiMH |
|---|---|---|---|---|
| Environmental Safety | ✅ Sealed, no spills | ❌ Risk of acid leaks | ⚠️ High resource impact | ✅ Safe |
| Maintenance | ✅ No water topping needed | ❌ Regular water checks are required | ✅ No maintenance | ✅ No maintenance |
| Energy Density | ⚠️ Low to moderate | ⚠️ Low | ✅ High | ⚠️ Moderate |
| Initial Cost | ✅ Low to moderate | ✅ Low | ❌ High | ⚠️ Moderate |
| Cycle Life | ⚠️ Medium (200–500 cycles) | ⚠️ Low | ✅ High (1000+ cycles) | ⚠️ Medium |
| Safety | ✅ Very safe | ⚠️ Risk of hydrogen accumulation | ⚠️ Requires BMS | ✅ Safe |
| Typical Applications | UPS, telecom, wheelchairs | Automobiles | EVs, solar systems | Small electronics |
5. Where Are VRLA Batteries Used?
VRLA batteries are used across many sectors, thanks to their reliability and sealed design:
Uninterruptible Power Supplies (UPS)
Telecommunications base stations
Solar and wind energy storage systems
Emergency lighting & alarm systems
Mobility equipment (wheelchairs, scooters)
Forklifts and floor scrubbers
6. Final Thoughts: Why Choose VRLA?
VRLA batteries strike an ideal balance between cost, reliability, and maintenance.
They are:
Senza manutenzione
Environmentally friendly
Easy to install
Safe and sealed
Cost-effective for backup and stationary use
Although they may not offer the same cycle life or energy density as lithium-ion batteries, VRLA batteries are trusted worldwide for backup, storage, and off-grid power systems where safety and simplicity matter most.
References & Further Reading:
Battery Council International (BCI). Lead-Acid Battery Technical Manual.
Sonnenschein Battery Datasheets.
Gates Energy Products. Absorbent Glass Mat (AGM) Technology Overview, 1971.
U.S. Department of Energy: Energy Storage Database.
IEC 60896-21 & -22: Stationary Lead-Acid Batteries Standards.
