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Easy DIY: Ecodiesel Main & Auxiliary Battery Replacement Guide (10 Steps)

  • Writer: Muddy Ruttzz
    Muddy Ruttzz
  • Nov 18
  • 6 min read

Why Your Jeep Gladiator Battery Replacement Can’t Wait


When it comes to car batteries a 3 year warranty means 3 years and it pays to swap them out before you get left stranded. In this DIY article I will tell you exactly how to swap both batteries and show you with lots of detailed photos to make it easy.


We came out to the garage to use our Gladiator the day before our big Ouray Jeep Jamboree trip, hit the start button and nothing. Over the last year or so I've been getting a warning on the dash that said, "Auxiliary switches unavailable, battery charging" so this battery issue was not a big surprise.  My decision to prioritize installing Spicer Performance Diff Covers for the Ouray trip now seemed a little misguided. I should have been thinking "batteries." I was left scrambling to do a main & auxiliary battery replacement so we could leave the next day on a trip that was planned for a year.


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White Jeep with pop-up tent on top, parked in a forest. A ladder leads to the tent. Sunlight filters through trees. Text: "Willys," "Muddy Ruttzz Overlanding."
Our 2020 Wrangler was pretty new when we took this trip to California's Hendy Woods State Park to see Old Growth Redwoods several years ago. This was the trip I forgot the ladder. Fortunately I remembered as we passed Santa Rosa and stopped to buy one at a local store.

I Swapped Batteries On My 2020 Wrangler Ecodiesel At 3 Years As A Act Of Preventive Maintenance


My 2020 Wrangler got new batteries at 3 years. I didn't wait for anything to go wrong, I just did it at three years. This whole stop start system was kind of new at the time and reading Jeep forums I saw many owners batteries were going bad. In fact lots of them were replaced under warranty. I bit the bullet and swapped them out to avoid being stranded in a remote overlanding location. I didn't take my own advice with the Gladiator but now I was forced. Thank goodness it was in the garage when it wouldn't start. The good news, this simple Jeep Gladiator Ecodiesel battery replacement is something any owner can handle.

Gloved hand near tool cart with batteries, wrenches, and a magnifying glass. "Super Start" and "The Legend" labels visible. Tire in background.
I chose this Napa Legend Battery - Its a powerful 800 Cold Cranking Amps and it fits exactly.

Car battery labeled NAPA Legend Premium AGM. Warning labels and barcode visible. Close-up of battery connections. Black casing with red handle.
Use a AGM battery - they have better shock and vibration resistance. This is a 94R H7 and fits perfectly in the battery tray.
Car battery labeled "Super Start" with red and black terminals, set in a black compartment. Visible wires and metallic connectors nearby.
This AUX 14J AGM fits in the Auxiliary Battery Compartment

Step 1: Picking Batteries That Will Start My Diesel Even When Its Cold

Believe it or not I have not and have no plan to eliminate the Stop Start Battery on our Gladiator. I know it really aggravates a lot of Jeep owners but I have heard some of the methods to do it have unintended negative consequences. So I am replacing both. I like Napa and this 800 Amp Napa Legend Battery is a good price and has a good warranty. Most importantly it has worked very well for me on the Wrangler. If you want to understand battery group sizes check out this Battery Council International Article.

Jeep with open hood in a garage. Text highlights hood access and windshield protection. Mirror reflects Jeep. Calm setting.
Open that hood all the way to get at the batteries! Protect the windshield.

Step 2: Hood Wide Open To For Access Main & Auxiliary Battery For Replacement


A person wearing gloves works on a car battery. Tools and red wires are visible. A badge reads Outdoor Adventure, Muddy Rutzzz.

Step 3: Disconnect The Main Battery Leads

Danger! Your vehicle is still energized until the Auxiliary Battery is disconnected. Remove the Negative Lead first and zip tie it out of the way. Remove the Positive Lead and zip tie it out of the way being sure it does not make contact with the negative lead or any metal parts of the vehicle. Arcing can damage the electronics on your vehicle.

A battery thermo cover in a engine bay. Text reads Battery Thermo Cover and Muddy Ruttzz Logo is visible.
Thermo Cover Protects From Extreme Heat And Cold

Step 4: Remove the battery thermo cover, set it aside and replace it with the new battery. It is important to the battery's longevity.

Gloved hands use a wrench to remove a battery hold-down in a car engine bay. Text: "Remove Battery Holdown." Label: "Outdoor Adventure Muddy Rutizz."
Use a extension and a 10 mm socket to remove the battery hold down bolt.

Socket extension and long bolt is visible and plastic part. Text reads Hold down bolt (long bolt) and Battery Holdown. Muddy Ruttzz Logo is visible.
After removing the battery hold down bolt the plastic battery hold down can be removed.

Car battery being removed. Text reads "Pull Battery Out (it's heavy)." Red cables visible. Tools nearby in the vehicle engine bay.
Now you can pull the battery out but it is pretty heavy.

Step 5: Remove The Battery Hold Down And The Old Battery


Black metal plate with 2 bolts. Text reads Auxiliary Battery Compartment. Muddy Ruttzz logo is visible.

Car battery with a red terminal and black lead in a dusty compartment. Text: "Disconnect and Separate Aux Battery Leads." Logo bottom left.
Just like with the main battery leads the negative should be removed first and leads need to be isolated so no arcing occurs.
Battery compartment with wires and connectors, featuring a red cap. Text reads "Hole In Bottom Is Battery Vent" with a logo at the corner.
Pull the battery out and but be sure the leads don't ground out.

Step 6: Remove The Auxiliary Battery

Gloved hands handle car batteries on a workbench. A red arrow points to the terminals. Text reads: "Posts (2) must be transferred..."
Posts must be transferred from old aux battery to new. As far as I know nobody sells these specialized posts so it is important to save these and install them on the new battery.

Car battery with posts highlighted by arrows, text advises using a 4mm socket to remove them. Background shows tools and labels.
My first time I used Vise Grips to remove these then I realized a 4 mm 6 sided socket fit them perfectly.

Step 7: Transfer The Small Posts From The Old Aux Battery To The New Aux Battery


Battery terminals and text instructions on transferring terminals. Left: “Remove This Nut.” Right: Gloved hands prying clip.
I left this terminal on till the battery was removed to make it easier to access the plastic clip that hooks on the backside of the battery. Remove it and reinstall it on the new main battery.
Wire brush cleaning a metal terminal; text says "Use a Wire Brush to Clean Terminal Where it Contacts Post." Background tools visible.
This is a good time to clean any oxidation off the terminal where it contacts the battery post.

Step 8: Remove Main Battery Terminal From Old Battery - Reinstall it on New Main Battery


A person installs a new auxiliary battery in a vehicle. Text reads "Install the New Aux Battery." The glove and battery stand out.

Close-up of a gloved hand holding a plastic cover with arrows pointing to "Reinstall Cover" and "This Plastic Part Holds Down The Aux Battery."
This plastic tube holds down the Aux battery and stops it from bouncing around inside the battery bay.
Arm with black glove using a red power tool on a vehicle engine. Dirty components surround. Badge reads “Outdoor Adventure Muddy RuTzz.”
Installing the bolts in the aux battery cover.

Step 9: Installing New Aux Battery (Reversing The Process)


Gloved hand near a car battery labeled "Legend." Text reads "Don't Make This Mistake!" Industrial setting, red cable, overhead view.
I installed the battery upside down, terminals are on the wrong side.
Gloved hand points at car battery with "Correct Installation" text. Dirty metallic car interior, red cable visible, adventurous logo bottom-left.
Battery installed correctly
Car battery with thermo cover in a vehicle, red terminal cover visible. Text reads "Thermo Cover Installed Terminals Reconnected."
Battery Installed, thermo cover installed and battery terminals reconnected.

Step 10: New Main Battery Installed And A Lot Of Money Was Saved In The Process





Car engine close-up with text: "3 Year Warranty On New Batteries (I find they last 3 years)." Background shows engine details and pipes.


Conclusion:

All right, ready to see if this bad boy starts up. Success! The Jeep starts up now. I think this Gladiator is going to be running strong on our trip to Ouray, Colorado. This was a easy DIY project that saves a lot of money. The batteries are pretty expensive all by themselves so if you have to pay to have it done it will cost a small fortune. If you attempt this project after reading this article I hope my photos and details have helped you out.


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