A battery is a device that stores electrical energy in the form of chemical energy and releases it when needed. It works by converting chemical energy into electricity through electrochemical reactions. One common type of battery is the lead-acid battery, which is widely used due to its reliability and cost-effectiveness.
The lead-acid battery consists of two electrodes: a negative electrode made of sponge lead (Pb) and a positive electrode made of lead dioxide (PbOâ‚‚). The electrolyte is a dilute sulfuric acid solution, typically between 22% and 28%. During charging, electrical energy is converted into chemical energy, while during discharging, the stored chemical energy is transformed back into electricity. When the battery is discharged, the lead at the negative electrode undergoes oxidation, forming lead sulfate (PbSOâ‚„), while the lead dioxide at the positive electrode is reduced to lead sulfate as well.
During charging, the reverse process occurs. The lead sulfate on both electrodes is converted back into lead and lead dioxide, restoring the battery’s ability to store energy. This makes the lead-acid battery a secondary battery, meaning it can be recharged multiple times. A single lead-acid cell provides about 2 volts, and multiple cells are often connected in series to increase the voltage. For example, three cells in series provide 6 volts, while six cells in series give a 12-volt system commonly used in cars.
To maintain performance, distilled water should be added periodically to replenish the electrolyte level, ensuring the sulfuric acid concentration remains within the optimal range. Proper maintenance helps extend the battery's lifespan and ensures reliable operation.
The chemical reactions involved in discharging are as follows:
Discharge reaction: PbO₂ + 4H⺠+ SO₄²⻠+ 2e⻠→ PbSO₄ + 2H₂O
Negative electrode reaction: Pb + SO₄²⻠- 2e⻠→ PbSO₄
Overall reaction: PbO₂ + Pb + 2H₂SO₄ ⇌ 2PbSO₄ + 2H₂O
(The reaction proceeds to the right during discharge and to the left during charging.)
Battery Applications
Lead-acid batteries come in various types, each designed for specific applications:
- Starter batteries: Used for starting vehicles such as cars, motorcycles, tractors, and diesel engines.
- Fixed batteries: Serve as backup power sources in communication systems, power plants, and computer networks.
- Traction batteries: Power electric vehicles, forklifts, and other industrial equipment.
- Railway batteries: Provide power for lighting, starting, and auxiliary systems in locomotives and passenger cars.
- Energy storage batteries: Used for storing energy from renewable sources like wind and solar power.
The main components of a lead-acid battery include the positive and negative plates, the electrolyte, the battery case, and separators. The positive plate is made of lead dioxide (PbOâ‚‚), the negative plate is made of sponge lead (Pb), and the electrolyte is a mixture of sulfuric acid (Hâ‚‚SOâ‚„) and water (Hâ‚‚O).
Common Battery Use Errors
1.1 Mismatched Battery Capacity with Engine
Choosing a battery with an appropriate charge capacity based on the engine type and usage conditions is essential for maximizing battery life and efficiency. If the battery has too low a capacity, it may overheat and suffer internal damage during high-current starts, especially in cold weather. On the other hand, a battery with excessive capacity may not be fully utilized, reducing its overall efficiency. Therefore, selecting the correct battery capacity is crucial for proper performance and longevity.
1.2 Parallel Connection of Batteries
Some users connect a fully charged battery in parallel with a weak one to start the engine. However, this can cause uneven current distribution, leading to damage or reduced lifespan of the weaker battery. Instead, it is better to replace the weak battery with a fully charged one before attempting to start the vehicle.
1.3 Mixing New and Old Batteries in Series
Using new and old batteries together in series can reduce their lifespan. New batteries have lower internal resistance and higher voltage, while older ones have higher resistance and lower voltage. This imbalance leads to improper charging and discharging, potentially causing overcharging or deep discharge, which can damage the battery and even reverse its polarity. Always use batteries of the same age and condition in series.
1.4 Continuing to Use Damaged Battery Cells
In diesel vehicles, two 12V batteries are often connected in series to provide 24V for starting. If one battery is damaged, some drivers may short-circuit it, which can create dangerous current imbalances and damage both the battery and the generator. It is important to replace or repair any damaged battery immediately and avoid using it in a shorted condition.
1.5 Ignoring the Venting Hole
The venting hole allows gases produced during charging to escape safely. Ignoring it can lead to pressure buildup inside the battery, increasing the risk of rupture or explosion. Always ensure the venting hole is clear and properly maintained.
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