Why Do Some Jeeps Have Two Batteries?

With its origins dating back to the battlefields of World War II, the Jeep brand holds a unique place in history among American automakers. So much so that some name the brand's initial U.S. Military offerings as the country's greatest contribution to warfare as we know it in the modern world. Given the context, it's no surprise that the Jeep brand is one that's often associated with innovation, particularly when it comes to the 4x4 arena.

These days, of course, the greater Jeep lineup stretches far beyond the long-discontinued CJ models and the Wrangler-styled Jeeps that helped put the company on the automotive map. At present, there are just as many sport utility vehicles in the Jeep lineup as there are traditional Jeeps, and there's even a pickup truck-styled version of the Wrangler build. The company has continued to innovate with each model year, and today some of the Jeeps in the lineup boast so many modern bells, whistles, and extras that they require additional power to ensure they all function as intended. 

It seems the solution to that particular power predicament led Jeep not to outfit their vehicles with a larger battery, but an additional one – there are actually some newer Jeep models that have two batteries under the hood. The second is there primarily to serve as an auxiliary power source ensuring the reliability of certain power-consuming features like the Electronic Start/Stop feature.

Not every make and model of Jeep is outfitted with two battery sources. As it stands, the second power source is primarily found in vehicles that have the ESS (Engine Start/Stop) function. That list includes many of the offerings in the current Jeep lineup, including the Grand Cherokee and Jeep Gladiator builds, among others. If you're not familiar with the start/stop system concept, it's the fuel-saving function on a Jeep that stops the engine from running while idling at stop lights and stop signs then restarts it when it's time to move again.

As you can imagine, that particular feature can be a legit battery drainer on larger vehicles with bigger engines, so Jeep was likely wise to outfit vehicles equipped with an auxiliary power source to help limit the possibility of a dead battery. But ESS is not the only function the second battery is meant to power, as Jeep vehicles with the eTorque feature also tend to have the auxiliary source.

Odds are if your Jeep has those features installed, you have a second battery in the vehicle. If you're still not certain, you can verify whether the battery is there by looking at your vehicle's owner's manual to confirm its existence and location. However, there may or may not be a diagram in that owner's manual that shows you precisely where the second battery is located in your Jeep. But even if that diagram is not there, you should be able to find the battery yourself. 

To be clear, locating the second battery on your Jeep may not be quite as easy as just raising the hood and pointing it out with the naked eye. There is, after all, limited room under the hood of most vehicles, and in terms of the Jeep, that essentially meant the auxiliary battery could not be set up right next to the primary power source. If there is a diagram in your Owner's Manual, you likely noticed the smaller auxiliary power source is buried in a harder to reach location in the engine.

In some Jeep builds, the auxiliary battery may be located behind or underneath the passenger seat. However, in many builds, it's located underneath the vehicle's Power Distribution Center, which is better known as the fuse box. In any case, it's a black box affixed just behind the main battery, and to access the secondary battery, you'll likely need to remove the PDC altogether. Doing so will require a small bit of under-the-hood knowhow and a handy socket wrench to boot.

Once you've got the PDC and all the other protective plates out of the way, you should be able to see the little auxiliary battery underneath. But even if we fully understand the design needs to fit the secondary battery way down there, getting to it on the rare occasion that you need to jump or replace it looks to be a bit of a headache — even if its very existence could help lengthen the life of both batteries powering your Jeep.