JL JOURNAL : HOW TO Replace Main & Auxiliary Battery on a JL Wrangler / JT Gladiator


Staff member
Is it probable these 2018 batteries might had been sitting for some time before the JL was sent out? Lead acid batteries hold an expiration date before chemical process is deemed unable to hold a charge. If the acid is inactive, the lead is sulfated, or the plate contact is broken inside the cells it won’t charge. I was surprised about the plugs on the bottom of the fuse box.

Who could say for sure but I suppose it is possible.

Hey Eddie and Cindy,
Great video btw. Why Odessy batteries? I’m a bit shell shocked at the prices for a replacement. Is it really worth it? Yeah I know. It’s a Jeep... that’s what we do. But still thats another $300 plus. And apparently I’ll need a new one to avoid this happening again. Yeah again.

Also, any luck with dealership on a battery replacement?

I just had my Jeep towed to my mechanic for what ended up being a dead battery. They charged it overnight and now seems to run without issue. Even took it to the dealership. They re flashed the computer with an update that actually added a few minor new features on the screen. Dealership said it was an update issue that the computer was going weird prior to battery dying. I’m still scratching my head on that one. So no new battery from dealership for me. But at least I asked right[emoji20]

Also that type S charger looks like a must for me as well. Any issues with it?


I've had the Type S jump starter for over a year now and have used it a few times. No problems what so ever. I would highly recommend it.

Regarding batteries, you can find replacement batteries at O'Reilly, Autozone, Napa and the dealership and for less than an Odyssey. I prefer Odyssey because they're a good deep cycle battery and that's good to have for winching and if you run things like a fridge.


New member
Hmm maybe because your JK doesn't have stop start. If you had only one battery in your JL and stop start was going all the time you'll fry your computers in a couple years tops. Every time your jeep cranks there is a voltage dip. Then a spike when the cranking stops. No big deal on a vehicle that you start a couple times a day. Huge deal on a vehicle that can start dozens of times in an hour.

The two batteries disconnect during cranking. All the computers are on the small aux battery and then the big battery cranks the engine. Once it's up and running the batteries reconnect. That keeps the computers from seeing all the dips and spikes. Pretty simple to understand why it is the way it is when you know how it works.

What a total piece of shit Whap and Jew has engineered there. Total unneeded dog shit. My Jk only needs one battery, why does this dog turd need two? If they want to use two batteries, put them both up top like a diesel pickup. Like God intended. Oh well I don’t think my new Bronco will have a fucking abortion setup like this. In your driveway at 5 am in the fucking dark with -50 windchill blowing up your ass, that would be no fun!

Sent from my SM-G960U using JL Wrangler Jeep Forum mobile app


New member
The entire vehicle still runs on 12V. The 48v battery is the interface to the generator and then there is a 48v to 12v converter that charges the 12v battery from the 48v battery.
So what with the 2.0L. It is possible the 48v battery is the main power to the generator since there is no alternator. The 12v battery is only used at start up?

Sent from my iPhone using JL Wrangler Jeep Forum mobile app

Sent from my SM-G960U using JL Wrangler Jeep Forum mobile app


Resident Smartass
Just getting caught up over here. Been a while.

That looks like a pain in the ass!

2012 JKUR Billet Silver
2012 JK Dozer
1975 DJ5 Postal


Guy with a Red 2-Door
I think my aux battery is shot. Everyday we get in the Jeep the average mpg gets reset. We currently are getting 68mpg lol. Gas gauge is still reading full after a full week of driving. Gotta bring it in and have the dealer test it and the main battery.


Staff member
Eddie why are you showing a different jump starter in your store?
No comments about it, is it better?
Sorry about that. In the video's description, I note that it is better. The one shown in the video will work on a JL but the one I note to buy will start the V8 in my JK and even the diesel on my Duramax.