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Do SLA Batteries Need Venting?

Power - by Bryan Veldboom - updated on 2/1/2022

Person checking an SLA battery

At some point, you may have heard someone refer to the process of battery venting. Today we’ll be taking an in-depth look at battery venting. We’ll explain what it is, why it happens and how this process differs between different types of lead acid batteries.

What is Battery Venting?

Before we define venting, let’s take a moment to explain what lead acid batteries are. Lead acid batteries are used to power a variety of applications such as cars, trucks, boats and other vehicles, as well as things like electric wheelchairs, UPS backups and industrial scrubbers. When a lead acid battery recharges, electricity flows through the water portion of the battery’s electrolyte, dividing it into hydrogen and oxygen. For a more in-depth look at this process, you can check out the article entitled “How Does a Car Battery Work.

The important point for our purposes here is that hydrogen and oxygen gasses are both flammable and need to be removed from the battery. Venting is the process by which a lead acid battery releases these gasses in order to prevent them from building up pressure inside your battery. It does this through a vent cap located on the top of the battery, which allows gasses to seep through.

Lead Acid Battery Safety Tips

Since hydrogen and oxygen can be flammable, you need to be cautious when storing or recharging a lead acid battery. Make sure to store lead acid batteries in a well-ventilated area that’s located away from any sparks or open flames. You also want to be sure to keep the vent cap free of any obstruction. Be sure to wear personal protective gear when charging a battery, including acid-resistant goggles or a face shield, safety gloves and, ideally, a pair of safety shoes and an acid-resistant lab coat or apron.

If you use a battery charger, you need to be sure that it matches the voltage and chemistry of your battery. You’ll also want to be very careful not to overcharge your battery as this can cook the components inside and cause additional venting. Always disconnect the charger immediately once the battery is fully charged or pick up a battery maintainer that switches off automatically once the proper voltage is reached.

What are SLA batteries?

Sealed Lead Acid (SLA) batteries are also known as Valve Regulated Lead Acid (VRLA) batteries. These are just two different names for the same type of battery. For clarity’s sake, I’ll be referring to them here as SLA batteries. The biggest difference between SLA batteries and traditional lead acid batteries is that SLA batteries are sealed. This means that they don’t vent hydrogen and oxygen into the air during the recharging process. Instead, these gasses recombine into the electrolyte inside the battery, which is why SLA batteries don’t need to have distilled water added to them the way traditional lead acid batteries do. For a more in-depth look at this process, read our article titled “How Does an SLA Battery Work?

Does a Sealed Battery Need To Be Vented?

Even though they don’t release gasses on a regular basis, an SLA battery can still vent during certain situations. If the battery is overcharged, it can boil the electrolyte inside, producing too much pressure for the battery to hold onto. Likewise, if the battery is charged too quickly, the gas can build up faster than it is able to recombine with the water inside. If either of these situations occurs, an SLA will vent gasses through a one-way pop-off valve in the battery’s body.

For these reasons, you should follow the same safety standards as you would with a regular lead acid battery, storing your SLA battery in a well-ventilated area free of any sparks or open flames. You also want to be sure to use the proper charger and be careful to avoid overcharging your SLA battery.

Do Gel Batteries Vent?

Gel batteries are another type of Valve Regulated Lead Acid (VRLA) battery. Unlike other SLA batteries, the electrolyte inside a gel battery is mixed with a silica additive. This turns the electrolyte inside into a gel-like substance. Due to this unique design, gel batteries create a minimal amount of fumes, which reduces a gel battery’s need to vent.

Shop Batteries Plus for SLA Batteries, Battery Chargers & More

Shop our enormous selection of batteries for a huge range of applications both big and small. Batteries Plus has lead acid and SLA batteries for cars and trucks, boats, motorcycles, UPS backups, children’s riding toys and so much more. Need a new battery charger? We can help with that too. If you’re experiencing issues with the battery in your phone, car or other vehicle, bring it to your nearest Batteries Plus and have it tested for free. The majority of our locations also offer free car battery installation with the purchase of a new auto battery (good on most makes and models).

Want to learn more about lead acid batteries? Our blog has plenty of additional answers for you. Some related articles include “How Do Battery Charging Cycles Work?” and “How Do I Know if My SLA Battery is Dead?