What Is A Lead–Acid Battery?
Lead-acid batteries are electrochemical energy storage devices using lead dioxide (PbO₂) and sponge lead electrodes immersed in sulfuric acid electrolyte. They’re widely used in automotive starting, lighting, and ignition (SLI) systems, backup power supplies, and renewable energy storage due to their reliability, low upfront costs, and recyclability. These batteries operate through reversible redox reactions, achieving ~80-85% energy efficiency.
How do lead-acid batteries chemically work?
Their operation hinges on sulfation/desulfation cycles—discharging converts electrodes into lead sulfate (PbSO₄), while charging reverses this via external current. Electrolyte concentration fluctuates between 1.28-1.31 SG during cycles.
During discharge, lead dioxide (positive plate) and metallic lead (negative plate) react with sulfuric acid (H₂SO₄), producing lead sulfate, water, and electrons. Charging applies voltage to reverse this: PbSO₄ decomposes into Pb, PbO₂, and H₂SO₄. Pro Tip: Avoid discharging below 50% depth-of-discharge (DoD) to prevent permanent sulfation. For example, a 12V car battery at 10.5V risks plate corrosion. Transitionally, this chemistry explains why over-discharging kills lead-acid units—irreversible crystal growth reduces active material.
What are the types of lead-acid batteries?
Three primary variants exist: flooded (FLA), AGM (absorbent glass mat), and gel. AGM and gel are valve-regulated (VRLA), sealing electrolyte to enable maintenance-free operation.
Flooded batteries require periodic water top-ups but tolerate overcharging better. AGM types use fiberglass mats to immobilize electrolyte, offering higher power density and vibration resistance—ideal for motorcycles. Gel batteries thicken electrolyte with silica, excelling in deep-cycle applications like solar storage. Transitionally, AGM strikes a balance between cost and performance. Table 1 compares key attributes:
| Type | Cycle Life | Cost |
|---|---|---|
| Flooded | 200-300 | $100/kWh |
| AGM | 400-600 | $180/kWh |
| Gel | 500-800 | $220/kWh |
What are lead-acid batteries’ advantages and limitations?
Strengths include low upfront cost and high surge currents, while weaknesses involve weight (~15-30kg for 12V 100Ah) and shorter cycle life than lithium alternatives.
Lead-acid excels in cold cranking amps (CCA)—a 12V 70Ah car battery delivers 700A briefly to start engines. However, energy density is poor (30-50Wh/kg vs. 150-200Wh/kg for LiFePO4). Table 2 contrasts lead-acid with lithium:
| Metric | Lead-Acid | LiFePO4 |
|---|---|---|
| Cycle Life | 300-800 | 2000-5000 |
| Efficiency | 80-85% | 95-98% |
| Cost/kWh | $100-$250 | $400-$800 |
Practically speaking, why choose lead-acid for solar? Initial affordability outweighs longevity in budget setups. Pro Tip: Pair AGM batteries with solar charge controllers having temp compensation to prevent gassing.
How to maintain lead-acid batteries?
For flooded types: check electrolyte levels monthly, refill with distilled water, and clean terminals. Keep batteries fully charged when idle.
Equalize flooded batteries every 30-60 days—apply controlled overcharge (15.5V for 12V) to desulfate plates. Use a hydrometer to monitor specific gravity; deviations >0.03 indicate cell failure. Transitionally, maintenance impacts lifespan: neglected FLA batteries fail in 1-2 years versus 3-5 with care. Pro Tip: Install battery trays with spill containment for flooded types—sulfuric acid leaks corrode metal surfaces.
Where are lead-acid batteries still dominant?
Automotive SLI systems (75% market share), UPS backups, and off-grid solar due to established infrastructure and cost. Forklifts use heavy flooded units for ballast.
Despite lithium’s rise, lead-acid remains king for gasoline car starting—a $12 billion annual market. Why? Instant high-current bursts and tolerance to partial charging suit irregular engine use. Transitionally, submarines still use massive lead-acid banks (e.g., 126 cells in 360V systems) for silent operation. However, telecom towers now prefer lithium hybrids for longer backup runtime.
Redway Power Expert Insight
FAQs
Yes—fully charged (SG 1.30) electrolyte freezes at -70°C, but discharged (SG 1.10) freezes at -7°C. Always store charged.
Are lead-acid batteries recyclable?
Yes—98% of lead is recovered. Return spent units to certified centers to avoid environmental penalties.
Why does my battery swell?
Overcharging causes gas buildup—replace bloated batteries immediately; they risk exploding if ignited.