What Is An Aux Battery?

Last Updated on May 26, 2023 by Paul S.

My battery died on my Jeep!  No biggie I thought, I can swap that out in 10 minutes as soon as I get a ride to the auto parts store. As quick as that thought crossed my mind I also realized that my Jeep JL has an aux or an auxiliary batter!  Not going to be such a quick change if that aux battery needs a replacement as well. 

Modern automobiles are equipped with various electrical components and systems that rely on a stable power supply. While the primary car battery is responsible for starting the engine and providing power to the essential electrical systems, there exists another battery known as the auxiliary battery. In this article, I dive into the purpose of an auxiliary battery, how long it typically lasts, and which vehicles are equipped with one.

What is an Auxiliary Battery In A Car?

An auxiliary battery, also known as a secondary battery or accessory battery, serves a specific purpose separate from the primary car battery. Its primary function is to provide power to secondary electrical systems and devices when the engine is turned off or when the primary battery is unable to supply sufficient energy.

What Does An Auxiliary Battery Do?

1. Powering Secondary Systems: Auxiliary batteries are responsible for providing electricity to secondary systems that require continuous power, such as radios, entertainment systems, GPS units, security systems, and various aftermarket accessories like off-road lighting or refrigerators. 

2. Engine-Off Power Supply: In certain vehicles, especially those with start-stop technology, the auxiliary battery takes over the power supply when the engine is turned off to ensure uninterrupted operation of critical systems. This prevents unnecessary strain on the primary battery.

3. Emergency Backup: In case of a primary battery failure, the auxiliary battery can act as an emergency backup, allowing the driver to start the engine and continue the journey until the primary battery is replaced or recharged.

How Long Does An Auxiliary Battery Last?

The lifespan of an auxiliary battery can vary depending on several factors, including usage patterns, climatic conditions, maintenance practices, and the quality of the battery itself. On average, an auxiliary battery tends to last between 3 to 5 years. However, this estimate is only a general guideline, and individual experiences may vary.

It’s worth noting that auxiliary batteries are generally subjected to deeper discharges compared to primary batteries. This frequent cycling can impact their lifespan, leading to a shorter overall service life. Regular inspection, maintenance, and prompt replacement when signs of deterioration appear can help optimize the lifespan of an auxiliary battery.

Check out our article about how long your Jeep Wrangler Battery should last!

Vehicles with Auxiliary Batteries

While not all vehicles are equipped with auxiliary batteries and that is a good thing if you like to easily switch out your batteries yourself and save a little bit of money. They are commonly found in the following types of vehicles:

1. Hybrid and Electric Vehicles: Hybrid and electric vehicles extensively rely on auxiliary batteries to power various systems when the main battery is being charged or when the vehicle is in standby mode. These systems include air conditioning, lighting, infotainment, and other electronic components.

2. Recreational Vehicles (RVs) and Campervans: These vehicles are very power hungry because they are your home on wheels! RVs and campervans often feature auxiliary batteries to power onboard appliances, lighting, water systems, and other amenities when the vehicle is parked or disconnected from an external power source.

3. Off-Road and Overlanding Vehicles: Off-road enthusiasts and overlanding vehicles often incorporate auxiliary batteries to provide power for auxiliary lighting, winches, camping equipment, refrigeration, and other electrical accessories required during off-grid adventures. Some people can get carried away with their features on their rigs but that is a good thing!  But power will be needed!

Here are some of the SUVs that have an auxiliary battery:

  • Jeep Wrangler/Gladiator (check out this great aux battery for the Gladiator. We have no affiliation with this link it just has great reviews.) 
  • Toyota 4Runner
  • Ford Expedition
  • Chevrolet Tahoe
  • Nissan Armada
  • GMC Yukon
  • Land Rover Range Rover
  • Mercedes-Benz G-Class
  • BMW X7
  • Audi Q7

Is It Difficult To Change Your Auxiliary Battery?

Yes, it can be a lot more difficult to change your auxiliary battery in your vehicle than your main battery. Typically these batteries can be tucked away and requires a lot of removal of other parts to reach it. 

For example, the Jeep Wrangler JL has its auxiliary battery tucked under the main battery and you need to remove the wheel well guard to get access to it. It helps to have the wheel taken off or put on a lift for even greater access. But who has a lift sitting around their house!

How Much Are Aux Batteries?

The price of auxiliary batteries for vehicles can vary depending on the size, type, and brand of the battery. However, on average, auxiliary batteries can cost anywhere from $50 to $200.

Here are some factors that can affect the price of an auxiliary battery:

  • The size of the battery: Larger batteries will typically cost more than smaller batteries which is typically a no brainer right!?!?!
  • The type of battery: There are two main types of auxiliary batteries: AGM and flooded lead-acid batteries. AGM batteries are more expensive than flooded lead-acid batteries.
  • The brand of the battery: Some brands of auxiliary batteries are more expensive than others. Typically in the battery world you get what you pay for so if you need to depend on your aux battery in the wilderness for a long time it’s probably best to pay up!
  • The retailer: The price of an auxiliary battery can vary depending on where you purchase it.

What is an Aux Battery – Wrap Up!

Auxiliary batteries play a vital role in ensuring a continuous power supply for secondary electrical systems in vehicles. They serve as a backup source of energy, especially when the primary battery is unable to meet the demands or when the engine is turned off. Understanding the purpose and lifespan of an auxiliary battery can help car owners make informed decisions regarding maintenance, replacement, and optimizing the lifespan of this essential component.

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