Automotive Lead-Acid Batteries Structure Principle and Practical Guide

As the core energy storage component in automotive electrical systems, lead-acid batteries have long provided reliable power for vehicle starting, ignition, lighting, and various electrical devices, thanks to their mature technology, stable performance, and affordable cost. Their working mechanism and proper maintenance are directly linked to the vehicle’s normal operation. This article provides a comprehensive analysis from three perspectives: structure, working principle, and usage guidelines.

Core Structure: Precisely Coordinated Components

The stable operation of an automotive lead-acid battery relies on the synergistic cooperation of its components, with the design centered on the core requirements of energy storage and release.

Plate Groups

The plate groups, consisting of positive and negative plates, serve as the primary medium for energy conversion. Positive plates use lead-antimony alloy grids coated with brownish-red lead dioxide active material, while negative plates use the same alloy base coated with gray spongy pure lead. In each cell, there is one more negative plate than positive plates to ensure uniform discharge on both sides of the positive plates and prevent plate warping.

Separators

Separators are placed between positive and negative plates, made of insulating materials such as glass fiber or microporous plastic. They prevent direct contact and short-circuiting while allowing electrolyte ions to pass freely. Some separators feature grooves facing the positive plates to facilitate electrolyte circulation and settlement of shed active material.

Electrolyte and Container

The electrolyte is a diluted sulfuric acid solution prepared by mixing pure sulfuric acid with distilled water in a specific ratio, typically with a density of 1.24–1.30 g/cm³, providing the conductive medium for chemical reactions. The container is usually made of acid-resistant, shock-resistant ABS plastic or hard rubber, divided into 3 or 6 cells connected in series to produce a rated voltage of 6V or 12V.

Auxiliary Components

These include positive and negative terminals for external circuit connection, inter-cell connecting straps, safety valves for pressure control, and vent holes. The safety valve automatically releases pressure in case of abnormality to prevent swelling or explosion, while vent holes safely exhaust gases generated during reactions.

Working Principle: Reversible Conversion Between Chemical and Electrical Energy

The key advantage of lead-acid batteries lies in their reversible chemical reactions, enabling energy storage and repeated release.

Discharge Process

When the vehicle starts or electrical devices are in use, the battery discharges. Lead dioxide on the positive plates and spongy lead on the negative plates react with sulfuric acid in the electrolyte to form lead sulfate, releasing electrons that flow through the external circuit to supply power.

Charging Process

During engine operation, the alternator charges the battery. External electrical energy reverses the reaction, converting lead sulfate on both plates back to lead dioxide (positive) and spongy lead (negative), while restoring sulfuric acid concentration in the electrolyte, thus re-storing energy.

Key Characteristics

This reversible reaction allows repeated charging and discharging without memory effect, maintaining stable capacity without needing periodic deep discharges. The state of charge can be easily assessed by measuring voltage or electrolyte specific gravity, without requiring specialized equipment.

Usage and Maintenance: Key Practices for Extending Service Life

The typical service life of an automotive lead-acid battery is 2–3 years, but proper usage and maintenance can significantly extend it and prevent unexpected failures.

Proper Usage Guidelines

Avoid chronic undercharging, which occurs with frequent short trips, long-term parking, or low usage frequency, accelerating capacity loss. Prevent over-discharging by turning off headlights and accessories before leaving the vehicle and avoiding prolonged use of electronics when parked, as this can cause plate sulfation and increased internal resistance. Avoid abnormal charging: overcharging decomposes electrolyte water and corrodes plates, while undercharging leads to lead sulfate crystallization and reduced capacity.

Routine Maintenance Essentials

Regularly check electrolyte level, keeping it between the upper and lower marks; add only distilled water if low—never purified water or sulfuric acid. Keep the battery clean; wipe away spilled electrolyte with a damp cloth to prevent terminal corrosion. Ensure terminals and connections are tight to avoid poor contact and overheating. Securely mount the battery to prevent damage from vibration. For long-term vehicle storage, charge at least monthly to compensate for self-discharge. Charge in a well-ventilated area; for the first three charges, maintain 24–30 hours and avoid covering the battery for proper heat dissipation.

Performance Characteristics and Application Scenarios

Lead-acid batteries offer irreplaceable advantages in specific applications, despite certain limitations.

Key Advantages

Low cost with abundant raw materials; mature and reliable technology with excellent starting performance and high instantaneous current capability; wide temperature tolerance (−40°C to 60°C); high safety due to non-flammable electrolyte and low-voltage design reducing explosion risk.

Limitations

Lower specific energy, resulting in greater weight and volume; shorter cycle life compared to lithium batteries; potential environmental and health risks from lead and sulfuric acid leakage, requiring proper recycling.

Currently, lead-acid batteries are primarily used in starting systems of conventional internal combustion engine vehicles and as power sources for some low-speed vehicles, where their cost-effectiveness and reliable starting performance remain core strengths.