How Does an SLA Battery Work?

Despite the fact that their design is over 160 years old, SLA batteries continue to be popular because of their dependability and low cost. There are few other batteries that deliver bulk power as cheaply as a lead acid battery. This is because the materials used to make them are relatively common, unlike more modern batteries, such as lithium, which rely on rarer materials that result in a higher upfront cost. But how does an SLA battery actually work and how is it different from other lead acid options? Keep reading for answers to all of your SLA battery questions.

What Does SLA Mean on a Battery?

There are two basic types of lead acid batteries: vented lead acid batteries and Sealed Lead Acid (SLA) batteries, which are also known as Valve Regulated Lead Acid (VRLA) batteries. All lead acid batteries contain a solution made of water and sulfuric acid called an electrolyte which drives the chemical processes which create electrical current within the battery.

Vented lead acid batteries vent hydrogen and oxygen gas into the air during their recharging process. This gassing also causes water from the electrolyte to evaporate as well. Because of this, the owner of a vented lead acid battery will have to add additional distilled water in order to replace what has been lost.

SLA batteries function a bit differently. They have a sealed design, which doesn’t allow gasses to escape. Since an SLA battery contains most of these gasses, they will recombine into the electrolyte, with no loss of water during the recharging process.

There are many different categories of SLA batteries, each designed with different applications in mind. For a full breakdown of these different varieties and what they’re used for, read our blog article entitled, “Which Type of SLA Battery Does Your Business Need?”

What are the Different Parts of an SLA Battery?

SLA batteries are constructed of a number of important components that work together to produce electricity.

Cells - SLA batteries are divided into a number of different cells. Each cell contains several grids, which house a number of lead plates.

Plates - The plates are either positively or negatively charged. Positive plates are covered with a paste of lead dioxide and the negative plates contain a paste of sponge lead. The plates are arranged in an alternating pattern of positive and negative grids divided by separators.

Electrolyte - In each cell, the grids containing the plates are submerged in a solution of water and sulfuric acid called an electrolyte. The chemical reaction between the electrolyte and the battery plates produces the electricity used to power the application.

Battery Separators - The battery separators are positioned between the positive and negative plates to help prevent electrical short circuits within the battery cells. They’re made of a thin, porous material that allows ions to pass through, but they are not electrically conductive.

Case - The battery’s case houses all of the components of a sealed lead acid battery. SLA cases are typically made of an ABS plastic that is highly resistant to corrosive chemicals and impact-resistant as well.

Terminals - Terminals are the electrical contacts used to drive electric current into the application or back into the battery when it is being recharged. There is a positive terminal (typically denoted by the color red) and a negative terminal (typically denoted by the color black).

How Does an SLA Battery Produce Power?

An SLA battery is an electrochemical device that converts stored chemical energy into electrical energy when the battery is connected to an external load. Electricity is produced by the chemical reaction between the material on the plates and the electrolyte. When the battery terminals are connected to an external load, a circuit is completed between the positive and negative grids, causing electricity to flow. Here’s how the process breaks down:

• The electrolyte contains positively charged hydrogen ions and negatively charged sulfate ions.
• When you attach a load to the battery, the sulfate ions in the electrolyte move to the negative plates and give up their negative charge.
• The remaining sulfate combines with the active material on the plates to form lead sulfate. This weakens the strength of the electrolyte and the sulfate on the plates acts as an electrical insulator.
• The extra electrons travel out of the battery’s negative terminal, move through the electrical device that’s being powered and then back to the positive side of the battery.
• At the positive battery terminal, the electrons flow back in and are accepted by the positive plates.
• The oxygen in the lead dioxide reacts with the hydrogen ions to form water and the lead reacts with the sulfuric acid to form lead sulfate.
• The movement of ions throughout the electrolyte creates the current flow. As the cells begin to discharge, the number of ions in the electrolyte will decrease and the amount of active material that can accept them also decreases as it becomes coated with sulfate.
• This will continue until the battery’s voltage drops so long that it can no longer deliver electricity.
• When it reaches this point, the battery is discharged and the electrolyte more closely resembles water.

How Do You Charge an SLA Battery?

Charging an SLA battery reverses the process listed above by converting electrical energy from a charger back into chemical energy within the battery. In a vehicle, the battery is recharged by the alternator. However, if you’re using an SLA battery for another application, such as a wheelchair or generator, you’ll need to pick up a charger.

Batteries Plus has chargers for practically any application. Visit our chargers page online and select the application of your choice. From there, just select the brand and model of your device to receive a list of compatible chargers. There are a few important things to keep in mind when selecting a charger. Always be sure that it matches the chemistry and voltage of your battery. For instance, if you’re looking for a charger to use with a 12-volt AGM SLA wheelchair battery, you will need to find a 12-volt charger that’s compatible with AGM SLA batteries.

How Do I Know if My SLA Battery is Bad?

On average, an SLA battery should last between three and five years. Keep in mind that there are a number of factors that impact an SLA battery’s actual lifespan, including how well the battery is maintained and what temperatures it is routinely used in.

There are a number of signs that will tell you when an SLA battery is starting to die. If it’s having difficulty holding a charge or needs to be recharged sooner than it used to, there's a good chance it might need to be replaced. If the battery is leaking or features bloating or bulging on the case, that’s a sure sign that something is wrong and you’ll want to have it replaced immediately.

If you’re worried that your battery may be dying, you can test it yourself using a multimeter or bring it to any Batteries Plus and have it tested for free. One thing to note, deep cycle SLA batteries can’t be quick-tested the same way as an auto or motorcycle battery. If you’re having issues with a deep cycle battery, take note of its typical voltage and run time and our experts can compare this to the battery’s ideal performance statistics.

Batteries Plus is Your SLA Battery Headquarters

Shop our selection of SLA batteries. We offer general purpose, deep cycle, gel and high rate UPS options. If you have a question, contact the experts at your nearest Batteries Plus location or visit our Sealed Lead Acid Buying Guide online. Does your business rely on SLA batteries? Find out how you can cut your energy expenses by signing up for a free business account.