Lead acid battery: Everything you should know about it.

About Lead acid battery, While picking a battery for a specific application, you want one that fulfills all conditions.

Once you have your specifics, you must ensure you need a lead acid or lithium battery.

If lead acid, which one to pick, sealed or wet flooded?

What is a lead acid battery?

The lead acid battery is a rechargeable battery that functions with the chemical reaction between lead and sulphuric acid.

Here, the lead remains submerged in sulphuric acid, and the chemical reaction produces electricity, and the same chemical reaction is used to recharge the battery.

Materials used for the lead acid battery:

Lead peroxide is a hard, brittle, dark brown substance forming a positive plate.

Sponge lead: Pure lead in sponge form forms a negative plate.

Different types of electrolytes.

Types of lead acid batteries:

There are three main types:

What is a flooded battery/STD?

These are the most widely used lead acid batteries and comprise alternating positive and negative plates (i.e., Lead and lead oxide plates) dipped in electrolytes/dilute sulphuric acid (water and sulphuric acid).

They are known as flooded because the electrolyte is liquid and free to move.

The chemical name of this strong acid is H2SO4, and it is a good electrolyte.

The acid is ionized, and the hydration of ions releases heat; the ratio of water and acid in the lead acid battery is 3:1.

In a lead acid battery, two plates remain dipped in sulphuric acid. When the electric current passes between these two plates, the dilute acid splits into its ions, i.e., hydrogen (positive H+ ions) and sulfate (negative So4- ions).

When these ions reach the lead peroxide plate, the hydrogen ions take positive ions from it and become hydrogen atoms.

These atoms attack lead peroxide and create PbO and H2O. The PbO reacts with the acid (H2SO4), forming lead sulfate and water.

With this reaction, the lead converts into lead sulfate, and the chemical energy converts into electrical energy. 

On charging the battery, this chemical reaction is reversed; the lead sulfate converts into sulphuric acid and lead.

The water splits into oxygen and hydrogen ions, and a vent relieves pressure to prevent hydrogen ions accumulation.

With the loss of hydrogen ions, these ions cannot combine with oxygen to form water again, and these batteries require regular watering.

What is an AGM battery?

AGM or absorbed glass mat one is a sealed lead-acid battery containing glass mat as a solid electrolyte.

The fiberglass mat between the lead plates immobilizes electrolytes.

Further, the glass mat acts as a separator and insulator between the two plates (positive and negative).

The hydrogen and oxygen gas produced through chemical reaction does not go out due to the safety pressure valve; thus, they recombine on charging.

What is a Gel battery?

It is also a sealed battery filled with silica to solidify the electrolyte.

The silica gel and sulphuric acid in gel batteries keep the lead and active material in place.

The gel sticks onto the lead forming a single piece of electrolyte and plates.

The oxygen is produced during the chemical reaction of these batteries.

Due to the seal and pressure valve, the positive plate absorbs the oxygen from the negative plate.

When the hydrogen ions are released at the negative plate, they combine with oxygen to form water, thus.

There is no water loss in these batteries too.

When the lead acid battery is charged

During the charging of the battery, the electrochemical reaction reverses, i.e., the electrical energy is converted into chemical energy.

As the battery does not store electricity, it stores the chemical energy required to produce electricity.

You will need a charger with a voltage higher than the batteries to recharge a battery.

When you connect the charger, it reverses the current flow.

It creates negative ions at the negative plate, and positive ions get attracted to them.

As a result, the hydrogen reacts with lead sulfate and forms lead and sulphuric acid.

The hydrogen increases at the negative plate when most sulfate is used.

The oxygen from the water reacts with lead sulfate and converts it into lead oxide.

As a result of this chemical reaction, oxygen bubbles form near the positive plate, and the process is termed gassing.

Car battery charger

Car battery charger

Discharging a lead-acid battery:

Discharging happens when the battery gives power to a device. However, a battery may get discharged even when it is not used. 

The sulphuric acid in the battery causes two chemical reactions; one at the positive plate and the other at the negative plate.

At the positive plate, sulphuric acid reacts with lead oxide and forms lead sulfate, hydrogen, and oxygen ions.

At the negative plate, it reacts with lead, forming lead sulfate and a free electron.

The negative plate has excess negatively charged electrons in a fully charged situation, and the positive plate doesn’t have them, creating a potential difference between them.

This potential difference is referred to as the voltage, and a fully charged battery has a voltage of 12.7 volts.

Self-discharge of a lead acid battery:

Lead acid batteries undergo self-discharge or internal discharge when unused. The self-discharge generally happens at the rate of 1 percent/day.

However, the rate may increase or decrease with the rise and fall of temperatures.

Generally, lead acid batteries have a very small percentage of antimony in their plates (usually ¼%) because antimony stabilizes active material in the plate and enhances mechanical strength.

Due to this antimony, flooded lead acid batteries have a high self-discharge rate of around 10-40% per month.

So, you may not keep them long in unused condition.

You must have experienced that when you leave your vehicle unused for over two weeks.

On the other hand, AGM and gel batteries have lower self-discharge rates as they do not have antimony.

These batteries gave mechanical strength due to their primary electrolyte material, i.e., absorbed glass mat or gel.

Their internal discharge varies from 5 to 15 percent/month.

Whether a normal discharge or self-discharge of a battery, sulfation occurs in both situations; however, the higher the self-discharge, the more will be the sulfation.

Gel, AGM, and calcium batteries have lower sulfation as their self-discharge rate is lower than flooded lead acid batteries.

During sulfation, the lead sulfate is produced, which accumulates near plates. Leaving this lead sulfate near plates for a long time will form crystals on hardening.

When you charge the battery again, these hardened lead sulfate crystals fail to break down, causing issues with the battery charging.

Checking the car battery

Checking the car battery

STD Vs. AGM battery Vs. Gel battery

The main difference between flooded batteries and sealed batteries is that of electrolytes.

Batteries type
Flooded batteries/STD batteries
Sealed batteries/valve-regulated lead-acid (VRLA)/ sealed lead-acid  (SLA) batteries
AdvantagesWide availability; Low cost; Variable sizes and capacity available; Excellent deep cycle performanceExpensive than other solutions; Need SMART regulators and chargers; May damage with overchargingA little more expensive than AGM batteries; Lower performance during warm temperatures; May damage with overcharging
Disadvantages High maintenance and regular watering required; Need charging in ventilated rooms; Need to wear PPE while handling; May cause corrosion or even injury due to leakage or spills; May damage due to overcharging; High internal discharge rateExpensive than other solutions; Need SMART regulators and chargers; May damage with overcharging.Requires no maintenance, No watering; No spills and leakages; High resistance against extreme temperatures; Shock and vibration proof; Low internal discharge rates; Superior deep cycle performance; Low internal discharge rates; No corrosion; Safe solution and can be installed with sensitive equipment; No gassing occurs; Good charging capacity; Higher life expectancy; Better electrolyte volume. 
Applications Suitable for forklifts and other industrial equipment such as solar power energy, UPS, and carsSuitable for low-power equipment such as RVs, cars, cell phones, boats, wheelchairs, snowmobiles, ATVs, solar power, etc.Applications are similar to AGM batteries and can be used for floor scrubbers, walkie-packet jacks, etc.


AGM batteries are better than flooded batteries if you are ready to spend some extra on batteries.

However, AGM batteries are comparable to gel batteries as both offer the following benefits.

Hope the difference between all these batteries is now clear to you.

If you need help with the battery cables, contact Cloom.