Installing a Dual Battery System in a Jeep JK
- Author
- 9 hours ago
- 8 min read
Adding a second battery to a Jeep JK is one of those upgrades that makes a lot of sense if you spend time off-road, camping, or running accessories away from home.
With a winch, lights, fridge, air compressor, communications equipment and other accessories, it's nice to have some additional battery capacity. More importantly, a properly installed dual battery system means you can run those accessories without worrying as much about draining the battery you need to start the Jeep.
For my Jeep JK, I decided to replace the factory battery tray with a Rugged Ridge dual battery tray, use two Odyssey AG Extreme Series batteries, and manage the two batteries with a National Luna Dual Smart Isolator.
The result is a relatively clean installation that gives me a dedicated starting battery while still having a second battery available for accessories.
Why Add a Second Battery?
The main reason for adding a second battery isn't simply to have twice the battery power.
The real advantage is being able to separate the starting battery from the battery being used for accessories.
When the Jeep is running, the two batteries can be charged by the alternator. When the engine is off, the isolator separates them so that accessories connected to the auxiliary battery don't normally drain the starting battery.
That means I can spend some time at camp running things like lights or other 12-volt equipment without having to worry about whether the Jeep will start the next morning.
It's a simple idea, but when you're several miles down a trail, having a battery left to start the Jeep is pretty important.
Parts I Used
For this installation I used:
Heat-shrink and wiring protection
Basic hand tools
You'll also want to make sure the batteries you're using are compatible with the particular tray you're installing. There are several Odyssey battery sizes, and terminal locations can vary. I used the ODX-AGM34R Extreme series.
Before starting the installation, I would recommend laying everything out and checking how the batteries and cables will fit.
Note: This is a job that requires an intermediate skill level and it will take some time. It requires some slight modifications to the Jeep components as well. It took me a good couple of hours.
Removing the Factory Battery Tray
The factory tray is designed for a single battery, so the Rugged Ridge tray replaces it and provides the space needed for the two-battery setup. The Rugged Ridge mount comes with clear instructions with images to guide you but here are the steps.
The first step is removing the factory battery and battery tray.
Disconnect the negative terminal first, followed by the positive terminal.
Remove ground from the stud on the inner fender.
Remove the PVC hose from the filter box. Remove the air filter cover by unclamping the cover and removing the hose clamp on the throttle body. Remove the air filter and housing. The housing is held in by three rubber grommets on the bottom of the box. A rocking motion may be needed for removal of air box.
Remove the EVAP solenoid connector and the power junction connector. Slide the EVAP solenoid off the tab and move to the side.
Remove the power steering reservoir bolt and move the reservoir to the side. Remove the reservoir mounting bracket and set aside.
Release tabs that secure fuse box to hinged bracket and pull fuse box upward. Lay fuse box over the side of the fender. Loosen the bolt at the bottom of the battery that secures the battery to the factory tray. Remove battery from vehicle.
Remove factory battery box by removing the 3 nuts that secure the box to the fire wall and 4 bolts securing the box in the engine compartment. Save this hardware. It will be used to install the dual battery tray.
This is a good time to clean up the area and inspect the existing wiring. Since you're going to be adding another battery and quite a bit of wiring, it's much easier to deal with anything that needs attention while the tray is out.
After removing your factory battery box, mark a line about 1” past the fuse box mounting holes toward the battery compartment. Cut the box along this line and set the side that mounts the fuse box aside to be reinstalled later. The Rugged Ridge mount comes with clear instructions with images to guide you.
Installing the Rugged Ridge Dual Battery Tray
The Rugged Ridge tray goes into the factory battery location.
Before tightening everything down, I recommend loosely installing the tray and setting the batteries in place.
This gives you a chance to make sure everything fits before committing to the final installation.
Pay particular attention to the battery terminals and the hood clearance. You don't want a terminal or cable connection getting too close to the hood.
Once you're happy with the positioning, tighten the tray down securely.
The batteries should also be properly secured in the tray. You don't want either battery moving around on a rough trail.
Here are the detailed steps taken from the installation manual that you will receive with the tray.
Install the provided spacers onto the three mounting studs on the fire wall and mount the Dual Battery Tray using the 3 factory nuts and 1 factory bolt removed previously.
Install the front section of the factory battery box that was cut previously using factory hardware. Then install the Fuse Box Bracket included with the Dual Battery Tray using the 3 Bolts and Flat Washers. The hinged factory fuse box bracket can then be installed on top of the Fuse Box Bracket included with the Dual Battery Tray. Reconnect all connectors to the fuse box and snap it back into position.
Check for clearance around the base of the Dual Battery Tray. Install both batteries onto tray and secure into position using J-bolts and Battery strap. Slide EVAP solenoid over tab on Fuse Box Bracket. Reinstall air filter box to its original location.
Installing the Two Odyssey Batteries
With the tray installed, the two Odyssey batteries can be positioned in their respective locations.
For my setup, one battery is the primary starting battery and the other is the auxiliary battery.
The original positive battery OE connection is a tight fit with the new battery. Make sure it is not touching any engine components and has enough room to allow for engine movement.
I did not use the clamps that came with the tray. I ordered longer universal stainless steel J bolts as they worked better than the ones that were supplied.
Installing the National Luna Dual Smart Isolator
The National Luna Dual Smart Isolator is what controls the relationship between the two batteries.
This is also the time to think about where the National Luna isolator will be mounted.
I prefer to keep the wiring as clean and direct as possible, while also keeping the isolator and connections protected from heat and moisture, moving parts and anything that could potentially damage the wiring. Initially I had the isolator solenoid and controller mounted on top of the batteries. It worked fine for a couple of months but eventually the controller failed due to moisture ingress. I have since moved both components and mounted them on an L-shape bracket I mounted to the inner fender.
The isolator allows the batteries to be connected for charging when the Jeep is running, while separating them when the engine is off.
This is what prevents your accessory use from unnecessarily draining the starting battery.
Mount the isolator in a location that is reasonably close to the batteries and protected from excessive heat and water.
From there, the main battery cables connect the isolator to the two battery positive terminals according to the National Luna wiring instructions.
The kit comes with detailed instructions on how to wire the cables and wiring and includes all the parts needed.
The exact cable sizes and fuse requirements should be based on the isolator, battery configuration and the loads you're running. Don't undersize the cables simply because the batteries are close together.
The next step is to run the harness for the remote controller and display through the firewall as the remote can be mounted in the cab for easy access and control. There is a main harness that routes through the firewall below the battery tray. You can make a hole in the grommet to feed the controller harness through but make sure you seal it properly to prevent water from leaking into the cab and main wiring harness.
I mounted the controller on the center console.
Connecting the Batteries
This is the part where it's especially important to take your time.
The starting battery remains connected to the Jeep's original electrical system.
The auxiliary battery is connected through the National Luna isolator.
When the Jeep is running, the isolator allows the charging system to charge the auxiliary battery.
When the Jeep is turned off, the isolator separates the batteries so the auxiliary loads can use the second battery without normally pulling the starting battery down.
If you're adding accessories such as a fridge, lights, air compressor or other equipment, I prefer to connect those loads to the auxiliary battery rather than the starting battery.
That keeps the purpose of the second battery clear: it's there to run the stuff that doesn't need to keep the Jeep running.
Important note: If you have a winch installed, connect the winch to the starter battery. You usually leave the engine running to ensure you have all the power you need while winching and therefore it is better to power the winch from the primary battery.
Cable Routing and Protection
Don't overlook the wiring.
A dual battery system can carry a lot of current, so the cables need to be properly sized, securely connected and protected from abrasion.
Keep cables away from exhaust components, sharp edges, belts, pulleys and other moving parts.
Where a cable passes near metal, use suitable protection such as split loom or abrasion-resistant sleeving.
I also like to keep the wiring organized rather than simply having several large cables crossing over the batteries.
A clean installation isn't just about how it looks. Good cable routing makes it easier to troubleshoot the system later and reduces the chance of a cable getting damaged on the trail.
Testing the System
Before considering the installation finished, check all of your connections.
Make sure:
Both batteries are securely mounted.
All positive connections are tight and properly protected.
Negative connections are secure.
The isolator wiring matches the National Luna instructions.
Cables are protected from abrasion and heat.
Nothing can contact the hood when it's closed.
Accessories intended for the auxiliary battery are actually connected to it.
Start the Jeep and verify that the charging system is operating normally according to the National Luna manual and that the auxiliary battery is being charged through the isolator.
I also recommend checking the battery voltages with the Jeep off and again with it running. This gives you a good baseline for how the system is behaving.
Is a Dual Battery System Worth It?
For a daily-driven Jeep that never runs anything more than the factory electrical equipment, probably not.
For a Jeep that's used for overlanding and camping, I think it's a worthwhile upgrade.
Having a second battery gives you more flexibility when you're away from the pavement. More importantly, it gives you some separation between the battery that starts the Jeep and the battery you're using for your accessories.
That's particularly useful when you're spending several days away from a power source.
The Rugged Ridge tray also makes the installation relatively clean because everything stays under the hood rather than requiring a second battery somewhere else in the Jeep.
For my JK, the combination of the two Odyssey batteries and the National Luna isolator gives me a much better setup for the kind of traveling and camping I use the Jeep for.
It's one of those upgrades that you hopefully never need to rely on—but when you're sitting around camp several miles from the nearest town, it's nice knowing you've got some extra electrical capacity sitting under the hood.
A Note on Electrical Safety
A dual battery system involves high-current electrical connections. A short circuit on a battery cable can produce extremely high current and can cause wiring to overheat or start a fire.
Use appropriately sized cables, fuses or circuit protection where required, secure all connections properly, and follow the manufacturer's installation instructions for the National Luna isolator, batteries and tray.
If you're not comfortable working around high-current automotive electrical systems, this is one installation where having a qualified installer do the wiring is worth considering.
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