Lead-Acid Battery Manufacturing: From Basics to Mastery

In today's diverse new energy battery landscape, lithium-ion technology dominates. However, one secondary battery, born over 160 years ago, continues to hold an irreplaceable position in automotive, telecommunications, and energy storage—the lead-acid battery.

Since Gaston Planté invented the first lead-acid battery in 1859, this technology has leveraged mature engineering, exceptional cost-effectiveness, and reliable performance to become the world's highest-volume rechargeable battery. This article examines the core principles, structure, classification, and applications of lead-acid batteries.

1. Core Principles: Redox Reactions

Lead-acid battery charging and discharging fundamentally involve redox reactions between active materials on the electrodes and the dilute sulfuric acid electrolyte—the most clearly understood system among secondary batteries.

Key Components: The positive electrode is lead dioxide (PbO₂), the negative electrode is spongy pure lead (Pb), and the electrolyte is 25%-40% dilute sulfuric acid (H₂SO₄). Each single cell has a nominal voltage of 2V.

Charge-Discharge Logic: During discharge, active materials react with sulfuric acid to form lead sulfate, consuming electrolyte. During charging, lead sulfate is reduced back to lead dioxide and pure lead, restoring electrolyte concentration.

Key Difference from Lithium-Ion: In lead-acid batteries, the electrolyte directly participates as a reactant. In lithium-ion batteries, the electrolyte only serves as a conduction medium.

2. Core Structure: Four Key Components

Lead-acid batteries feature a simple, stable structure with four core components. The separator (diaphragm) is particularly critical for sealed lead-acid batteries.

Electrode Plates: Positive and negative plates are the core carriers of electrochemical reactions. Each plate consists of a lead alloy grid coated with lead paste active material. Plate quantity and surface area determine battery capacity.

Electrolyte: Dilute sulfuric acid serves as both ion conduction medium and core reactant. Its concentration and purity directly affect capacity, internal resistance, and cycle life.

Separator (Diaphragm): Positioned between plates, it prevents internal short circuits, adsorbs electrolyte, provides oxygen recombination channels, and supports plates to prevent active material shedding.

Battery Case and Cover: Acid-resistant plastic housing provides sealing and structural support. Valve-regulated batteries feature safety valves to prevent excessive pressure and minimize water loss.

Common 12V lead-acid batteries consist of six 2V single cells in series; 24V batteries contain twelve cells.

3. Main Classifications

Through a century of evolution, lead-acid batteries have developed three mainstream categories.

3.1 Flooded Lead-Acid Batteries

The most traditional type, with liquid electrolyte completely submerging the plates.

Advantages: Extremely low cost, exceptional high-current discharge, excellent heat dissipation, stable lifespan.

Limitations: Requires regular water maintenance, leakage risk, cannot be tilted.

Applications: Automotive and motorcycle starter batteries, forklifts, low-speed electric vehicles.

3.2 Valve-Regulated Sealed Lead-Acid (VRLA-AGM)

The current market leader, using AGM fiberglass separators with all electrolyte absorbed in a starved-electrolyte design, combined with one-way safety valves for maintenance-free operation.

Advantages: Fully maintenance-free, leak-proof, any-angle positioning, high oxygen recombination efficiency, minimal water loss, superior cycle life.

Limitations: Higher cost, sensitive to overcharging.

Applications: Automotive start-stop batteries, UPS systems, telecommunications base stations, emergency backup power.

3.3 Gel Lead-Acid Batteries

An upgraded VRLA type where electrolyte is mixed with fumed silica to form a non-flowing gel.

Advantages: Superior maintenance-free performance, longer deep-cycle lifespan, tolerance to overcharging/over-discharging, stable low-temperature performance.

Limitations: Highest cost, slightly weaker high-current discharge.

Applications: Outdoor telecommunications storage, off-grid photovoltaic systems, harsh environment backup power.

Lead-Carbon Batteries: An improved category adding activated carbon to the negative electrode, significantly enhancing fast-charging and deep-cycle lifespan (over 1,000 cycles), popular for energy storage.

4. Core Strengths and Weaknesses

Core Strengths

Exceptional Cost: Raw materials (lead and sulfuric acid) are common commodities. Cost per Wh is only 1/3 to 1/5 of lithium-ion, ideal for cost-sensitive applications.

Superior High-Current Discharge: Can deliver 10-20 times rated capacity instantaneously, easily powering automotive starter motors—a capability most lithium batteries cannot match.

High Safety: No thermal runaway, fire, or explosion risk. Production, use, and recycling are fully controllable.

Complete Recycling: Global recycling rates exceed 95%, the most mature closed-loop system among all batteries. Lead materials are indefinitely recyclable.

Core Weaknesses

Low Energy Density: Only 30-50 Wh/kg, far below lithium batteries. Unsuitable for lightweight, long-range applications.

Short Cycle Life: Flooded batteries achieve 300-500 cycles; premium AGM and lead-carbon reach 1,000-2,000 cycles—still far below lithium iron phosphate.

Environmental Risk: Lead is a heavy metal. Improper management during production and recycling can cause pollution.

5. Main Applications

Leveraging irreplaceable cost and high-current advantages, lead-acid batteries dominate:

Automotive: Nearly all vehicles use lead-acid for starting/auxiliary low-voltage systems.

Emergency Backup: UPS systems, data centers, hospitals, and banks primarily use AGM lead-acid.

Telecommunications: Base station backup power and outdoor site energy storage.

Low-Speed Power: Low-speed electric vehicles, tricycles, forklifts, golf carts.

New Energy: Photovoltaic and wind power storage, off-grid generation systems.

Conclusion

Lead-acid batteries are not obsolete—they are the optimal choice for applications requiring cost-effectiveness, reliability, and safety. With century-refined technology, exceptional cost performance, and comprehensive recycling, they remain the world's highest-volume secondary battery.

As lead-carbon and gel technologies advance, lead-acid batteries will deepen their presence in energy storage and low-speed power, complementing rather than being replaced by lithium-ion batteries, together supporting the new energy sector.