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VRLA (Valve-Regulated Lead-Acid) Battery

1. Definition

A VRLA battery is a sealed lead-acid battery with a pressure relief valve that prevents gas escape under normal operation. The two main VRLA types are AGM (Absorbent Glass Mat — see separate page) and GEL (gelled electrolyte). VRLA batteries are used for non-automotive applications: UPS, telecom, and standby power.

2. How It Works

VRLA batteries use oxygen recombination: oxygen generated at the positive plate during charging travels to the negative plate (through the glass mat or cracks in gelled electrolyte) and recombines to form water. This eliminates water loss and enables sealed, maintenance-free operation. The one-way valve opens only if internal pressure exceeds safe limits (7-25 kPa).

3. Construction

  • Compressed cell stack (AGM) or gelled electrolyte (GEL)
  • Pressure relief valve (Bunsen valve) per cell
  • Sealed case with no removable caps
  • Lead-calcium-tin grids for low gassing
  • Envelope separators for dendrite prevention

4. Materials

  • Positive plates: PbO2 on Pb-Ca-Sn grid
  • Negative plates: Sponge lead on Pb-Ca-Sn grid
  • Electrolyte: H2SO4 absorbed in glass mat (AGM) or gelled with silica (GEL)
  • Case: ABS or flame-retardant PP (UL94 V-0 for telecom)
  • Valve: EPDM rubber, one-way

5. Technical Parameters

  • Voltage: 12V (single block) or 2V (single cell)
  • Capacity: 1.2-200+ Ah
  • Design life: 5-20 years (depending on grade)
  • Operating temperature: -15degC to +50degC
  • Float voltage: 2.25-2.30 V/cell at 25degC
  • Self-discharge: <2% per month at 20degC

6. Advantages

  • Completely sealed — no maintenance, no watering
  • Can operate in any orientation (AGM only)
  • No acid spill risk
  • Low self-discharge
  • Long service life (10+ years for premium)
  • No special ventilation required

7. Limitations

  • Sensitive to overcharging (thermal runaway risk)
  • Higher cost per Ah than flooded
  • Limited high-current capability vs flooded
  • Capacity degrades at elevated temperatures
  • Cannot be opened for individual cell testing

8. Applications

  • UPS (Uninterruptible Power Supply)
  • Telecom base stations and data centers
  • Emergency lighting
  • Security and fire alarm systems
  • Solar/wind energy storage
  • Electric wheelchairs and mobility scooters
  • Railway signaling

9. Comparison

Feature VRLA (AGM) VRLA (GEL) Flooded
Maintenance None None Periodic watering
Orientation Any Upright only Upright only
Cycle Life Good Best Moderate
Cost $$ $$$ $

10. Testing

VRLA batteries tested per IEC 60896-21/22 (stationary), IEEE 1188 (telecom), and IEC 61056 (general purpose). Key tests: capacity at C10/C20, float current, high-rate discharge, internal resistance, thermal runaway sensitivity.

11. Manufacturing Considerations

VRLA manufacturing requires precise electrolyte filling control, compression control for AGM assembly, leak testing (helium or pressure decay), and extended formation with recombination conditioning.

12. OEM Considerations

Chengguang manufactures VRLA batteries for UPS, telecom, and standby applications. Contact for VRLA specifications.

VRLA models — available on request. Not automotive starting batteries.

Technical reference maintained by Chengguang Power Tech Co., Ltd..