What Are SLA Batteries?

Power interruptions can occur unexpectedly due to factors that include inclement weather, fuses or overheating. These incidents have the potential to cause data loss, significantly disrupting your customer's network operations. As an installer, you can avoid these vulnerabilities by using a reputable battery backup source such as Sealed Lead Acid batteries (SLA) for many applications. SLA batteries are fully sealed and leak-proof, which makes them an ideal option for various applications — unlike traditional batteries.

This article will cover SLA batteries in their entirety, including the types, construction, applications and best practices to use for optimal performance in your projects. It will also explore how to charge and replace SLA batteries when required.

Read on to learn more about SLA batteries and how they can improve your next project installation.

What are Sealed Lead Acid (SLA) batteries?

SLA batteries, also known as Valve Regulated Lead Acid (VRLA) batteries, are rechargeable batteries composed of lead plates and sulfuric acid. They are designed to seal in electrolytes and provide electrical energy. SLA batteries offer secondary or backup power to a wide range of essential systems and equipment, from emergency lighting systems and video surveillance to fire alarm systems and access control.

SLA batteries have been around for over 160 years and carry numerous benefits, which include durability, cost-efficiency and longevity. Their vast range of availability, minimal maintenance requirements and safety features have made them a preferred power solution choice for many years.

What are Valve Regulated Lead Acid (VRLA) batteries?

Valve Regulated Lead Acid (VRLA) is another way of describing SLA batteries. The term “Valve Regulated Lead Acid” refers to the one-way pressure relief valve inside the battery that prevents the gas from leaking.

The two terms are interchangeable. However, "SLA battery" remains the more commonly used term for this type of rechargeable battery.

Main features of SLA batteries

SLA batteries have a great number of features that make them a preferred option for installers in different use cases, which include security, EVs, UPS systems and other backup applications. The features are as follows:

• Maintenance-free: SLA batteries have a sealed lead construction which prevents acid and gases from leaking out, eliminating the need to add electrolytes or water regularly. However, regular monitoring is still recommended.
• Leak-proof: The sealed lead construction of the batteries means they do not require any special handling or shipping containers.
• Safety features: An emergency pressure release system in the battery activates a small pressure release valve during over-charging. This safety vent regulates and releases gas pressure, safeguarding against potential battery damage.
• Wide temperature range: SLA batteries run at an optimal temperature of 20 to 25°C (68 to 77°F).
• Low self-discharge rate: The average self-discharge rate is only 4% to 6% per month, depending on battery type and ambient temperature. This also extends SLA battery shelf life, where they can last around 10 to 12 years.
• Deep discharge recovery: Many SLA batteries have advanced plate composition and balanced electrolyte systems that improve recovery from deep discharges.

However, installers must also keep in mind that these batteries have certain disadvantages. These include the following:

• Bulky size: The batteries are usually bulkier and heavier than traditional batteries because of their lower energy density.
• Environmental concerns: The lead component of the battery poses great concern to the environment in terms of recycling and lead exposure if mishandled.

Types of SLA batteries

SLA batteries offer remarkable versatility, making them suitable for a wide range of projects — from small-scale residential installations to large commercial jobs. When selecting an SLA battery, it's essential to consider the different types of battery and its applications. There are three main types, each with distinct features. Let's consider each of them in turn.

General purpose batteries

General purpose SLA batteries are commonly used in a variety of applications due to their reliability. They are frequently used in emergency lighting systems, including exit signs and lights for critical emergencies. Additionally, they are utilized as a UPS battery backup for small businesses, residential sump pumps and security systems such as surveillance cameras, fire alarm control panels and access control systems. When the main power supply is interrupted in such areas, the SLA battery takes over, allowing users to still gain access to secured areas.

General purpose SLA batteries are affordable, easily rechargeable, have a wide temperature range and can be stored for extended periods, making them adaptable in both residential and commercial applications.

Deep cycle batteries

Deep cycle SLA batteries are specifically designed to provide consistent power over a longer period than general purpose SLA batteries. The term "Deep Cycle" means that they can handle deep discharges of 80% to 100%. The Depth of Discharge (DoD) can tell you how much of the battery capacity is being utilized. Their design is typically smaller in size than regular SLA batteries and has thicker lead plates to generate more electricity in the battery. This helps with handling deep discharges over time, which keeps equipment running all day long.

Deep cycle SLA batteries are ideal for applications that require sustainable power output. Deep cycle SLA batteries are useful for remote monitoring systems in locations with limited access. Additionally, they provide uninterrupted service to UPS systems, ensuring continuous power for equipment like computers, servers and communication systems.

High-rate UPS batteries

Engineered with thinner cell plates than deep cycle batteries, high-rate UPS batteries deliver high bursts of power for short durations, making them suitable as starter batteries for emergency situations. High-rate UPS batteries serve as a quick solution in situations where sudden power disruptions occur, preventing data loss and preventing production downtime or safety hazards. These batteries provide backup power for applications including fire alarm systems, surveillance cameras, UPS systems for data centers, medical emergency equipment, data comm and networking devices such as network switches and routers.

This battery type can help your customers save time and money by preventing costly equipment damage and business disruption. High-rate UPS batteries also have a lifespan of up to 10 years, which is longer compared to other SLA batteries.

How to charge an SLA battery

There are several ways to charge a Sealed Lead Acid battery. For installers, it is important to understand the different charging techniques for SLA batteries to improve the shelf life. Below are some ways to charge SLA batteries:

• Constant current: A commonly used method of charging SLA batteries. With this method, you run a constant current through the battery for a certain period of time.
• Constant voltage: In this method, instead of a current, you keep a constant voltage running through the battery. This is another popular method, although it requires proper voltage and timing settings to prevent overcharging.
• Taper current: This is not recommended for charging SLA batteries, as it can curtail the shelf life. However, if using this method, ensure that you have a charging cut-off circuit to prevent overcharging of the battery.
• Two-step constant voltage: This method is recommended for rapidly charging SLA batteries and then maintaining them in a fully charged (standby) condition.

SLA battery care and maintenance

With proper maintenance, Sealed Lead Acid batteries can last for years. However, charging mistakes can leave the battery defective. As an installer, it is essential to follow good charging practices to prolong the health of SLA batteries. Here are a few tips to keep in mind:

• Always store the battery fully charged to avoid complete depletion over time.
• Avoid leaving the battery fully discharged for an extensive period, as this can result in capacity loss or damage for some SLA batteries. However, this rule does not apply to deep cycle SLA batteries, as they are designed to withstand multiple deep cycles.
• Avoid overcharging the battery, as this can lead to overheating and shorten battery life or damage it.
• When charging your SLA battery, always make sure to match the correct battery charger's voltage and current to the voltage of the battery you are charging to avoid battery failure.

When to replace SLA batteries

Most SLA batteries have a lifespan of three to five years (300 to 500 cycles). This, of course, can vary depending on factors like charging methods, environment, applications and battery quality. Recognizing when to replace an SLA battery is crucial for your customers to prevent equipment service disruptions. What follows are some common signs to watch for:

• Inability to hold a charge for an extended period
• Rapid drop in voltage levels
• Physical damage, such as bloating or swelling, which indicates overcharging and will require immediate replacement

Once an SLA battery has reached the end of its lifespan, it is considered hazardous waste. So, what is the correct method for disposing of it? As SLA batteries contain lead, it's best to recycle them in accordance with local guidelines and regulations to reduce their environmental impact.

Overall, SLA batteries provide reliable backup power for various applications, offering versatility, quality performance, durability and longevity. By understanding their types, construction and maintenance practices, you can successfully utilize SLA batteries in your projects and ensure uninterrupted service for your customers.