What is a Lead-Acid Battery?
A Lead-Acid Battery is a type of rechargeable battery that uses lead and lead dioxide as electrodes and sulfuric acid as the electrolyte. These batteries have a wide range of applications, such as in vehicles, uninterruptible power supply (UPS) systems, power backup systems in alarms, solar applications, golf carts, and more.
Generally, lead-acid batteries have a basic construction that consists of individual primary cells or cells, each with 2V, connected in series within the same casing. In large battery systems, these cells are independent units that are also interconnected in series through bridges, forming a bank.
Each cell consists of a positive electrode, which is a lead plate coated with lead dioxide, and a negative electrode, which is a porous lead plate immersed in a diluted sulfuric acid solution.
What types of Lead-Acid batteries are there?
According to needs and applications, there are two main types:
Open Lead-Acid Batteries:
In this type of batteries, the electrolyte is a diluted sulfuric acid solution that is free between the electrodes. These batteries require periodic maintenance to check the electrolyte level and add distilled water if necessary. Types of open batteries include:
- Starting batteries: the most common type of lead-acid battery used in motor vehicles to provide the necessary power to start the engine.
- Deep-cycle batteries: capable of supporting multiple charge and discharge cycles, suitable for applications like electric vehicles, golf carts, and solar power systems.
- Stationary batteries: used in stationary applications, such as backup power systems and telecommunications.
Sealed or Valve-Regulated Lead-Acid (VRLA) Batteries:
In this type of battery, the electrolyte is immobilized in a gel or fiberglass. This eliminates the need for periodic maintenance and makes the batteries safer. Types of sealed batteries include:
- Absorbed Glass Mat (AGM) batteries: the electrolyte is absorbed in a fiberglass mat, providing greater resistance to vibrations and overcharging.
- Gel batteries: the electrolyte is in gel form, offering greater resistance to leaks and overcharging.
- Enhanced Flooded Battery (EFB): a type of open battery with an improved separator that reduces the need for maintenance.
The choice of the right lead-acid battery type depends on the specific application.
The choice of the right lead-acid battery type depends on the specific application. Next, we will look at the advantages and disadvantages of AGM and gel batteries.
What's the difference or advantages and disadvantages between gel lead-acid batteries and AGM lead-acid batteries?
Gel lead-acid batteries and AGM (Absorbed Glass Mat) lead-acid batteries are both sealed with a valve regulator (VRLA) to release gases generated during charging, but they have some differences:
Gel Lead-Acid Battery:
- Electrolyte: They use a gel-form electrolyte, a gel-like substance that thickens. The gel surrounds the plates and prevents the movement of the electrolyte inside the battery.
- Plate structure: They have thicker plates compared to AGM batteries.
- Energy density: They tend to have a lower energy density than AGM batteries due to their thicker plates.
- Life cycles: They tend to have a slightly longer life cycle compared to AGM batteries, especially in deep discharge and frequent recharge applications.
- Vibration resistance: They are usually more resistant to vibration due to their thicker plates and gel electrolyte.
- Cost: Although it can vary and depend on factors like brand, capacity, and design, they are generally more expensive than AGM batteries.
AGM Lead-Acid Batteries:
- Electrolyte: They use a fiberglass-saturated acid-absorbed separator between the plates to absorb and retain the electrolyte. Although the electrolyte is present in liquid form, it is contained in the separator and cannot easily spill.
- Plate structure: They have thinner plates and are generally closer together compared to gel batteries.
- Energy density: They have a higher energy density due to their thinner plates and more compact arrangement.
- Life cycles: Although they can offer good performance in deep cycles, some AGM batteries may have a slightly shorter lifespan than gel batteries under certain conditions.
- Vibration resistance: While robust, AGM batteries may be more sensitive to vibration compared to gel batteries in some applications.
- Cost: They are more economical than gel batteries.
The choice between gel batteries and AGM batteries depends on the specific needs of the application, environmental conditions, and user preferences. Both types are sealed and maintenance-free, making them suitable for various applications.
What is a VRLA Lead-Acid Battery?
Although we mentioned the term VRLA in the previous section, we will expand on this information:
VRLA stands for "Valve Regulated Lead-Acid" and refers to a type of lead-acid battery design. VRLA batteries are sealed and use a regulating valve to control the release of gases generated during the charging process. These batteries are also known as sealed lead-acid batteries and are part of the lead-acid battery family, which includes gel batteries and AGM batteries.
Key features of VRLA batteries:
- Sealed: VRLA batteries are designed to be sealed, meaning that the electrolyte (sulfuric acid solution) is encapsulated and cannot escape under normal conditions of use. This design has several advantages, including eliminating the risk of acid leakage and the ability to mount the battery in various positions.
- Regulating Valve: VRLA batteries incorporate a safety valve that regulates internal pressure and allows controlled release of gases produced during charging. This prevents excessive pressure buildup inside the battery.
- Absorbed or Gel Electrolyte: VRLA batteries can have lead plates immersed in an absorbed electrolyte (as in AGM batteries) or in a gel (as in gel batteries). Both designs help keep the electrolyte in place and contribute to making the battery leak-resistant.
- Common Applications: VRLA batteries are used in a wide variety of applications, including backup power systems, uninterruptible power supplies (UPS), solar power systems, recreational vehicles (RVs), among others.
The VRLA designation is a broad term that encompasses both gel batteries and AGM batteries, as both share the characteristic of being sealed and regulated by valves. These batteries are appreciated for their maintenance-free design, installation versatility, and reliable power supply across various applications.
