What Is a Lead Acid Battery?

Lead acid batteries are among the oldest and most reliable rechargeable battery technologies available today. 

Invented in 1859 by French physicist Gaston Plante, these batteries continue to be widely used in various applications due to their dependability and cost-effectiveness.

In this article, we’ll look at what lead acid batteries are, how they work, and their various applications.

How Lead Acid Batteries Work

A lead acid battery is a rechargeable battery that uses lead and sulfuric acid to function.

In its most basic form, this popular type of battery consists of lead plates (negative) and lead dioxide plates (positive) submerged in an electrolyte solution of sulfuric acid. This arrangement allows for a controlled chemical reaction that produces electricity.

The battery operates through a reversible chemical reaction. 

During discharge, the lead from the negative plate and lead dioxide from the positive plate react with the sulfuric acid to form lead sulfate and water. 

This reaction releases electrons, creating an electric current. When charging, this process is reversed: the lead sulfate converts back to lead, lead dioxide, and sulfuric acid.

The 3 Components of a Lead Acid Battery

The primary active materials in a lead acid battery include:

• Lead peroxide (PbO2): A dark brown, hard substance that forms the positive plate

• Sponge lead (Pb): Pure lead in a soft, spongy condition that creates the negative plate

• Dilute sulfuric acid (H2SO4): The electrolyte solution that facilitates the chemical reaction

These components are arranged in alternating layers of positive and negative plates, separated by porous material to prevent short circuits while allowing the electrolyte to flow freely between them.

The 2 Types of Lead-Acid Batteries

Lead acid batteries come in several varieties, each designed for specific applications. 

But these two types that follow are the main versions you’re likely to encounter whether you’re shopping for home/personal devices or those for your business.

Flooded (Wet Cell) Batteries

Flooded lead acid batteries are typically used in situations where cost is the most important factor to consider.

Their distinctive feature is that they contain liquid electrolytes that freely surround the plates.

These batteries require regular maintenance, including checking the electrolyte level and adding distilled water as needed. 

Furthermore, you must keep them upright to prevent leaking. 

Sealed and Flooded Lead Acid Batteries

Sealed lead acid (SLA) batteries are designed to be maintenance-free and spill-proof (hence the “sealed” part).

Unlike the flooded batteries we just covered, the electrolytes in SLAs are either absorbed in a plate separator or formed into a gel. These batteries can be further categorized into:

• Absorbent Glass Mat (AGM) Batteries: These contain glass mat separators that absorb the battery acid, making them spill-proof and allowing them to be mounted in various positions.

• Gel Batteries: These contain silica to stiffen the electrolyte solution into a gel-like substance, making them ideal for deep cycle applications and environments with extreme temperatures.

Charging and Discharging Cycles

Alright, now that you have a better understanding of this particular type of battery, let’s dig into their charging and discharging processes, as this is crucial for maximizing the lifespan of lead acid batteries.

Charging Process

When a lead acid battery is charged, an external power source reverses the chemical reaction that occurs during discharge. 

In short, this is when the charging process converts electrical energy from the charger into chemical energy stored in the battery. 

During charging:

• Lead sulfate on the negative plate is converted back to lead

• Lead sulfate on the positive plate is converted back to lead dioxide

• Water in the electrolyte is converted back to sulfuric acid

As the battery approaches full charge, hydrogen and oxygen gases may be produced in a process called "gassing." 

In flooded batteries, this results in water loss that must be replenished.

Discharging Process

Then, during discharge, the battery functions as a galvanic cell, with the following reactions occurring:

• At the negative plate, lead reacts with sulfate ions to form lead sulfate

• At the positive plate, lead dioxide reacts with hydrogen ions and sulfate ions to form lead sulfate and water

As the battery discharges, the concentration of sulfuric acid decreases, and the specific gravity of the electrolyte falls. This change in specific gravity can be used to determine the state of charge in flooded batteries.

Applications of Lead Acid Batteries

Alright, now let’s get into the most important topic for the majority of you: what applications make the most sense for Lead acid batteries.

This could be broken down into two main divisions:

Starting, Lighting, and Ignition (SLI)

The most common use of lead acid batteries is in vehicles for starting the engine, powering lights, and supporting the ignition system. 

And this makes sense because these batteries are designed to deliver a high burst of power for a very short duration of time but are then continuously recharged by the vehicle's alternator.

Deep Cycle Applications

Deep cycle lead acid batteries are designed to provide steady power over a longer period and can be deeply discharged and recharged many times. 

This type is commonly used in:

• Golf carts

• Electric vehicles

• Marine applications

• Renewable energy storage systems

• Uninterruptible power supplies (UPS)

Maintenance and Care

As with any type of battery, proper maintenance and storage is vital to getting your money’s worth. 

Here’s what that looks like for lead acid batteries:

• Avoid deep discharges below 20% of capacity

• Recharge batteries promptly after use

• Keep batteries clean and free of corrosion

• Ensure proper charging voltage

• For flooded batteries, check and maintain proper electrolyte levels

• Store batteries in a cool, dry place

Fortunately, proper maintenance isn’t a time-consuming, expensive prospect, but that definitely doesn’t make it any less important.

Power and Energy Considerations

Lead acid batteries offer different performance characteristics depending on their design:

• Power density: The ability to deliver high current in short bursts

• Energy density: The amount of energy that can be stored per unit volume or weight

While lead acid batteries have lower energy density compared to newer technologies like lithium-ion, they excel in applications requiring high power density, reliability, and cost-effectiveness.

Equalization Charging

Equalization is a controlled overcharge performed periodically on flooded lead acid batteries. This process helps prevent stratification (uneven distribution of acid concentration) and sulfation (formation of lead sulfate crystals). 

During equalization, the charging voltage is increased for a short period, causing the battery to gas and mix the electrolyte.

Environmental Considerations

Lead acid batteries are among the most recycled consumer products, with a recycling rate of over 99% in many countries. The lead, plastic, and acid can all be recovered and reused in new batteries, making them an environmentally responsible choice when properly recycled.

Need Help Selecting Lead Acid Batteries?

Lead acid batteries remain a cornerstone of energy storage technology despite being one of the oldest battery types. 

Their reliability, cost-effectiveness, and recyclability ensure they will continue to play an important role in numerous applications for years to come. Understanding how these batteries work and how to properly maintain them can help users maximize their performance and lifespan.

While we hope this blog has helped, we also have a team of experts with decades of experience here to assist, as well. So, please feel free to reach out with any questions.