Battery Vent Tube: Why It’s Important For Safety

Why Some Car Batteries Require a Vent Tube

Many carmakers install the car battery in the truck, under the back seat, or inside the front fender. All lead-acid car batteries create hydrogen gas when charging. If the gas pressure gets too high, the battery will vent the gas into the atmosphere. That’s not a problem if the battery is located under the hood because there’s enough air movement to render it harmless. But when the car battery is mounted in a closed location, carmakers install a battery vent tube to route the hydrogen to the exterior so it doesn’t explode. It’s a safety issue.

The Role of a Vent Tube in Car Batteries

A vent tube is designed to safely channel gases produced inside the battery out of the battery housing and away from the vehicle’s interior. This feature is particularly important in certain types of sealed lead-acid batteries, like AGM batteries, which are commonly used in modern vehicles.

1. Gas Accumulation and Pressure Build-up: In sealed batteries, the gases generated during the charging and discharging process are usually recombined internally to form water, which prevents the electrolyte from drying out. However, in some circumstances, such as overcharging or excessive heat, the internal pressure can rise, causing the gases to accumulate faster than they can recombine. Without a means to safely vent these gases, the pressure could build up inside the battery, potentially causing it to swell, leak, or even burst.

The vent tube provides a controlled path for these excess gases to escape, reducing the risk of internal pressure build-up. By directing the gases out of the battery and away from critical vehicle components, the vent tube plays a vital role in maintaining battery safety and longevity.

2. Safety Concerns with Hydrogen Gas: Hydrogen gas, one of the primary gases produced during the battery’s operation, is highly flammable. In enclosed spaces, such as the engine compartment or the cabin of a vehicle, hydrogen gas can pose a significant safety risk if it accumulates and ignites.

The vent tube helps mitigate this risk by allowing the hydrogen gas to be safely expelled from the battery and directed to the outside of the vehicle, where it can dissipate harmlessly. This is particularly crucial in vehicles where the battery is located in a confined space, such as under the rear seat or in the trunk, where ventilation may be limited.

3. Preventing Acid Damage: In the event of a battery malfunction or overcharging, the vent tube also helps prevent the release of sulfuric acid vapors into the vehicle’s interior. Sulfuric acid is highly corrosive and can cause damage to metal components, electrical wiring, and upholstery. By directing any potential acid vapors away from the vehicle’s sensitive areas, the vent tube helps protect the vehicle from corrosion and other forms of damage.

The new battery will have vent ports on either side

Vented batteries are designed with two vent ports, one on each end of the battery. The battery is delivered with one port plugged and the other open. This design allows the installer to

Move the red plug to the unused vent port

mount the battery in the proper orientation and use either side to connect the battery vent tube simply by removing the plug and placing the plug on the opposite side.

How to install a car battery using the battery vent tube

Situate the battery in the battery tray with the posts in the proper orientation to connect to the battery cables.

Secure the battery hold down brackets/devices. Tighten until the battery doesn’t move, but do not over tighten. You only need enough torque to prevent battery movement. Over torquing the hold-down devices can crack the battery case.

Determine which vent port to use for the existing vent tube. If the port is plugged, twist the plug as you pull it out. Move the plug to the open port. Then, insert the battery vent tube into the open port.

Replace the tube if it’s damaged or missing

If the battery vent tube is damaged or missing or the elbow is broken, you can purchase a replacement battery vent tube kit at any auto parts store.

I strongly recommend replacing the vent tube if yours is missing or damaged.

This Dorman brand vent tube kit is just $12 at Autozone

©, 2023 Rick Muscoplat