The Jeep JL auxiliary battery group size is 400. Unlike many vehicles, Jeep Wrangler JLs have two 12-volt batteries—the primary battery is used to start the car, while the auxiliary battery is used to power vehicle accessories, like the radio and headlights.

While 12-volt

batteries

supply power to nearly all modern vehicles, there are significant differences between individual car batteries. And your car will likely require a different battery size than your neighbor's truck. Because of this fact, it's crucial that you purchase the correct battery when it's time to replace yours.

Today, we'll break down everything you need to know about the Jeep JL auxiliary battery size so you can confidently maintain your vehicle.

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How big is a Jeep JL auxiliary battery?

The auxiliary battery in a Jeep JL is group size 400.

The physical dimensions for your Jeep Wrangler JL auxiliary battery are 5-¾ inch x 5-⅞ inch x 3-7⁄16 inch. The battery weighs around 11.5 pounds and is capable of producing 200 cold cranking amps (CCA).

Battery replacements are one of the more expensive forms of

routine vehicle maintenance

. And when your car has two batteries to replace—like the Jeep Wrangler JL—the expenses can add up quickly.

Fortunately, if you drive a newer Jeep JL, a replacement battery might be covered under Jeep's three-year/36,000-mile basic warranty. If your Jeep needs a new battery and is less than three years old and has fewer than 36,000 miles, the cost to replace it might be covered under warranty.

However, if your car is outside that window, you'll most likely have to pay for the replacement battery yourself. You can expect to pay around $110 for a new group size 400 auxiliary battery like

this one

from O'Reilly Auto Parts.

What is the average lifespan for a Jeep JL auxiliary battery?

While the average 12-volt car battery typically lasts around three to five years, auxiliary batteries are usually smaller and have a shorter lifespan. You can generally expect an auxiliary battery to last between two and three years.

However, many factors affect a battery's lifespan, including the type of battery, your driving habits, and your location. And while all batteries will degrade over time, there are some steps you can follow to keep them in good shape and increase their lifespans.

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How to keep Jeep JL auxiliary battery healthy

Because battery replacements are such an expensive form of maintenance, it's vital that you take preventative measures to prolong your battery's life and avoid an early replacement. And because your Jeep JL has two batteries, it's especially prudent to make those batteries last as long as possible.

While this article focuses on your Jeep's auxiliary battery, the methods described below can and should be applied to your primary battery as well.

To get the most out of your battery's lifespan, follow these steps:

Start the engine regularly. If you let your Jeep sit for an extended period, you can almost guarantee that the battery is going to die. Even if you don't need to drive anywhere, start your JL up periodically and let it run for a few minutes to protect the battery.

Park your Jeep indoors whenever possible. Extreme weather contributes to battery degradation. While it may not always be possible to avoid poor weather depending on where you live, you should park indoors whenever you can to protect your battery.

Keep the battery secure.

Potholes

and bumps on the road can jostle your battery loose, eventually causing damage to its internals. Check your battery and its tie-downs occasionally to ensure that it is safe and secure.

Test the battery proactively. Proactively testing your battery is a great way to get out in front of any future issues.

Keep the terminals clean. It may come as no surprise that corrosion is bad for your battery. You should regularly check to make sure the terminals and cables are clean. But you can go one step further by purchasing a can of terminal protectant and spraying it on the terminals and cables every few months.

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