What Is A Battery Lead Acid Battery?
Lead-acid batteries are electrochemical energy storage devices using lead dioxide (PbO₂) and sponge lead (Pb) electrodes submerged in sulfuric acid electrolyte. Invented in 1859, they remain widely used for automotive starting, lighting, and ignition (SLI), backup power systems, and deep-cycle applications. These batteries offer low cost, high surge currents, and recyclability but require maintenance to prevent sulfation and electrolyte stratification. Modern variants include flooded, AGM (absorbed glass mat), and gel types, with lifespans ranging from 3–15 years depending on depth of discharge (DoD) and temperature management.
How do lead-acid batteries generate electricity?
Lead-acid batteries produce power through reduction-oxidation reactions between lead plates and electrolyte. During discharge, PbO₂ (positive) and Pb (negative) convert to PbSO₄, releasing electrons. Charging reverses this via external voltage. Sulfation—crystal buildup on plates—is a key failure mode if batteries sit partially charged. Pro Tip: Keep batteries above 12.4V (50% SoC) to minimize degradation.
When discharging, the positive plate’s PbO₂ reacts with H₂SO₄ electrolyte to form PbSO₄, water, and free electrons. Simultaneously, the negative Pb plate also forms PbSO₄. This dual sulfation reduces electrolyte density from ~1.28 to 1.10 SG. Charging applies voltage to split PbSO₄ back into Pb, PbO₂, and H₂SO₄. But why does sulfation occur? If left discharged, PbSO₄ crystals harden, reducing capacity. For example, a car battery left uncharged for months might drop from 650 CCA to 300 CCA. Pro Tip: Equalize flooded batteries every 10 cycles to rebalance cell voltages.
What are the types of lead-acid batteries?
Lead-acid variants include flooded (liquid electrolyte), AGM (fiberglass mat absorption), and gel (silica-thickened electrolyte). AGM excels in vibration resistance, while gel suits deep-cycle solar storage. Flooded types dominate automotive markets due to lower cost.
Flooded batteries use liquid electrolyte that requires periodic water topping. AGM batteries immobilize acid in glass mats, enabling spill-proof operation—ideal for boats or RVs. Gel batteries add silica to the electrolyte, creating a semi-solid paste that resists stratification but is sensitive to overcharging. For instance, a motorcycle using an AGM battery handles bumps better than flooded. Pro Tip: Use gel batteries for solar setups with inconsistent charging—they tolerate partial states better.
| Type | Maintenance | Cycle Life |
|---|---|---|
| Flooded | High | 200–500 |
| AGM | None | 400–600 |
| Gel | None | 500–1,200 |
What factors affect lead-acid battery lifespan?
Key factors include temperature, depth of discharge, and charging voltage. High heat accelerates corrosion, while deep discharges below 50% SoC accelerate sulfation. Ideal operating temps are 20–25°C.
Elevated temperatures above 30°C double corrosion rates—every 8°C rise halves lifespan. Conversely, sub-zero temps reduce capacity by 20–40%. DoD is critical: cycling to 80% DoD (20% SoC) yields ~500 cycles, but limiting to 50% DoD extends cycles to ~1,200. Imagine a golf cart battery: shallow discharges daily last 5 years, while deep drains might fail in 18 months. Pro Tip: Install temperature compensation on chargers—reduce voltage by 3mV/°C/cell above 25°C.
| DoD | Cycles | Capacity Loss |
|---|---|---|
| 20% | 1,500 | 10%/year |
| 50% | 600 | 15%/year |
| 80% | 300 | 25%/year |
How should lead-acid batteries be charged?
Use three-stage charging: bulk (constant current), absorption (constant voltage), and float. Bulk charges at 10–25% C-rate until 70–80% SoC, absorption tops up at 14.4–14.8V (12V system), and float maintains 13.2–13.8V.
Bulk mode pushes maximum current until voltage hits ~14.4V. Absorption then holds voltage while current tapers—this replenishes the last 20% capacity. Float maintains charge without overcharging. But what if you skip absorption? Undercharged batteries sulfate faster. For example, a forklift battery charged only in bulk loses 30% capacity in 6 months. Pro Tip: For AGM, set absorption voltage to 14.7V—higher than flooded’s 14.4V—to penetrate glass mats.
Are lead-acid batteries environmentally safe?
While 99% recyclable, improper disposal risks lead pollution and acid leaks. Modern recycling smelts lead, reuses plastic cases, and neutralizes acid into water. Always return batteries to certified centers.
Recycling recovers 95% of lead and 70% of sulfuric acid. However, informal recycling in developing countries releases lead dust, harming local communities. For perspective, the U.S. recycles 2.8 million tons annually, but 15% still end in landfills. Pro Tip: Check EPA-certified recyclers—illegal dumping incurs $10k+ fines. Transitionally, lithium-ion is displacing lead-acid in EVs, but cost keeps lead dominant in SLI roles.
Battery Expert Insight
FAQs
Yes, but handle cautiously—swelling indicates gas buildup. Transport upright to avoid leaks.
Do lead-acid batteries work in cold climates?
Yes, but capacity drops 20–40% below -20°C. Use AGM for better performance.
Can I mix flooded and AGM batteries in a system?
No—charging profiles differ. Mixing causes under/overcharging.
Are “maintenance-free” lead-acid batteries truly maintenance-free?
Most are sealed AGM/gel types but still require voltage checks and cleaning.
Why are lead-acid batteries cheaper than lithium-ion?
Mature manufacturing and recyclability keep costs at $100–$300/kWh vs lithium’s $150–$500/kWh.