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Lead-acid batteries: Science and technology

How lead plates in acid store energy, and why lead harms

What this tab covers The physics and chemistry: how the energy is stored, which materials it needs (scarcity, toxicity, recyclability) and what makes it age.

Lead-acid is the oldest rechargeable chemistry in wide use, one in which both electrodes turn into lead sulphate as the battery discharges. It is cheap per unit and very recyclable, but heavy, short-lived when cycled daily, and built on a toxic metal.

Mechanism

Mixed

The positive plate is lead dioxide and the negative plate is spongy lead, both sitting in dilute sulphuric acid. On discharge both plates react with the acid to form lead sulphate and the acid weakens; charging reverses this. Because the electrolyte itself takes part in the reaction and lead is heavy, energy per kilogram is low: 25 to 50 Wh/kg against 150 to 300 Wh/kg for lithium-ion. Variants include flooded cells (liquid acid, need topping up) and valve-regulated lead-acid (VRLA, sealed, with the acid held in glass mat or gel).1

Gravimetric energy density 25-50 Wh/kg1 Lithium-ion for comparison 150-300 Wh/kg1

Material scarcity and toxicity

Unfavourable

Lead is not scarce, and most of it is recycled, but it is a potent neurotoxin, especially for children, and sulphuric acid is corrosive. UNICEF and Pure Earth estimate that up to 800 million children, about one in three worldwide, have blood lead at or above 5 micrograms per decilitre (the level that calls for action), nearly half of them in South Asia; country estimates from the same report, as reported by Down To Earth, put about 275 million in India, and a 2018 meta-analysis found Indian children's average blood lead at about 6.9 micrograms per decilitre; unsafe informal recycling of lead-acid batteries, which handles up to half of them in low- and middle-income countries, is a leading cause. The EU sets the toughest rules of any chemistry for lead: 75% recycling efficiency by end-2025 and 80% by end-2030, 90% lead recovery by end-2027 and 95% by end-2031, and 85% recycled lead in new batteries from 2031.49101112

Children with blood lead at or above 5 micrograms/dL (global) up to 800 million9 Of which in India about 275 million10 Mean blood lead, Indian children (2018 meta-analysis) 6.86 micrograms/dL12 Share of lead-acid batteries recycled unsafely and informally up to 50%9 EU minimum recycled lead content (2031) 85%11

Degradation and ageing

Unfavourable

Lead-acid ages through sulphation (hard lead sulphate crystals that no longer recharge, worst when left partly discharged), corrosion of the positive grid, shedding of active material, and water loss. Life depends heavily on how deeply it is discharged. IRENA gives 250 to 2,000 cycles; PNNL's grid cost study used 675 cycles and a 12-year calendar life, at the low end of the literature, while listing a 10 MW, 50 MWh European system rated at 5,500 cycles at 50% depth of discharge. The US DOE says that at one cycle a day a lead-acid grid battery lasts only about 3 to 4 years.123

Cycle life range 250-2,000 cycles1 PNNL grid assumption 675 cycles, 12-year calendar life2 Life at one cycle per day about 3-4 years3

Lead-acid against newer batteries12

ChemistryEnergy densityCycle lifeRound-trip efficiency
Lead-acid25-50 Wh/kg250-2,000 cycles75-84% (PNNL literature range)
Lithium-ion150-300 Wh/kg1,000-12,000 cycles85-95%
Sodium-ion90-160 Wh/kg500-8,000 cyclesabout 92%

Sources

  1. Sodium-ion batteries: Technology brief (includes lead-acid and lithium-ion comparison data) IRENA, 2025
  2. Lead-Acid Battery methodology, 2020 Grid Energy Storage Technology Cost and Performance Assessment PNNL / US DOE, 2020
  3. 2022 Grid Energy Storage Technology Cost and Performance Assessment US DOE / PNNL, 2022
  4. EU Sustainable Batteries Regulation (2023/1542), policy summary International Energy Agency policy database, 2023
  5. A third of the world's children poisoned by lead, new groundbreaking analysis says (The Toxic Truth, UNICEF and Pure Earth) UNICEF, 2020
  6. A third of world's children are poisoned by lead, says UNICEF report Down To Earth (reporting UNICEF and Pure Earth), 2020
  7. Regulation (EU) 2023/1542 concerning batteries and waste batteries (Official Journal text) EUR-Lex, 2023
  8. A meta-analysis of blood lead levels in India and the attributable burden of disease (Ericson et al., Environment International 121, 461-470) Environment International, 2018