Remote start/ aux battery.

[frankjc]

I mentioned doing the aux battery delete, She wants me to replace the aux battery, I'm suggesting both. I can have the main battery load tested at work.
Thank you all for your input.

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[AndySpill]

I mentioned doing the aux battery delete, She wants me to replace the aux battery, I'm suggesting both. I can have the main battery load tested at work.
Thank you all for your input.

While you appreciate Frank my sentiment that the Aux battery is more trouble than its worth for owners committed to not running ESS events, my role is to advise, not insist.

Please appreciate, if you are doing this Aux battery replacement yourself that there are tools are parts (e.g. replacement plastic rivets) that one should have on hand if effecting this replacement from the ground as opposed as thru the engine bay.

Forum links on how to do this and battery suggestions, as well as Youtube videos are available on request.

One final thought: Last time I replaced my batteries I did so around the time of my annual inspection, which I failed initially because I deprived the vehicle of power and things needed to reset on my JL after about 100 miles of driving before I could then pass the inspection.

I don't no Mass. law on this as I suspect you do. If you have a hard deadline for inspection you may want to do that before battery replacement.

 

[entropy]

The main driver of the JLU is my girlfriend. She doesn't like the start stop feature. Her main concern is having the remote start working.

One battery dies. Eventually it takes the other and your jeep wont start. Replace both and press the button to turn off the feature anytime you start the jeep.

 

[AndySpill]

One battery dies. Eventually it takes the other and your jeep wont start. Replace both and press the button to turn off the feature anytime you start the jeep.

I'm sorry, I respectfully disagree. If you are committed to not running ESS events and press the button, either manually or by the purchase of tech to do so, or even a DIY solution, that ESS battery is more than not required, it's a burden.

I run both factory batteries and ESS. I have no horse in this race. I suggest people do what's best for them, not copy me if they have different priorities.

I will certainly concede that given the parallel connection of the two batteries, yes, either one going "sideways" can cannibalize the other, but logic and anecdotal evidence from the forum suggest the far smaller Aux one the more likely of the two to die and corrupt the main battery than vice versa.

 

[entropy]

I'm sorry, I respectfully disagree. If you are committed to not running ESS events and press the button, either manually or by the purchase of tech to do so, or even a DIY solution, that ESS battery is more than not required, it's a burden.

I run both factory batteries and ESS. I have no horse in this race. I suggest people do what's best for them, not copy me if they have different priorities.

I will certainly concede that given the parallel connection of the two batteries, yes, either one going "sideways" can cannibalize the other, but logic and anecdotal evidence from the forum suggest the far smaller Aux one the more likely of the two to die and corrupt the main battery than vice versa.

This is what I did in my 2019. I isolated the aux and kept it as a backup battery. But I no longer recommend this to people because of a couple reasons:

1) warranty. If theyre still under the short battery warranty window, it is best to leave the system alone.
2) the 2025 models, at least mine, swapped the negative wire connections. Meaning if you follow the directions posted here to isolate the aux you can end up unplugging the main negative. People can mess up. For example. If you then plug a battery charger to the unplluged negative and positive terminal you can end up frying something.

My 2025 had an unrelated electricsl issue and when I was talking to my dealers service advisor they asked if I tried isolating the aux. Told me they see jeeps dailys with fried electronics cause people try messing with the ESS.

If done correctly. Isolating the aux is the best you can do I agree. And you also end up with a backup starter battery as a plus. But people fuck up all the time, and the easiest for most is to simply swap both. A good pair should last a long time if ESS is deactivated.

 

[Heimkehr]

the 2025 models, at least mine, swapped the negative wire connections. Meaning if you follow the directions posted here to isolate the aux you can end up unplugging the main negative.

What does the suggested swap physically look like?

E.g., on my '21, the Negative cables for both batteries shared a single connection on the main battery's Negative post. The ESS battery cable was a bit thinner than the same for the Main battery, just enough to notice. Is the opposite now true?

 

[X35]

What does the suggested swap physically look like?

E.g., on my '21, the Negative cables for both batteries shared a single connection on the main battery's Negative post. The ESS battery cable was a bit thinner than the same for the Main battery, just enough to notice. Is the opposite now true?

Here is a photo of my 2025 negative battery connection. I believe the negative aux cable is the thinner one circled. Can anyone confirm?

 

[entropy]

What does the suggested swap physically look like?

E.g., on my '21, the Negative cables for both batteries shared a single connection on the main battery's Negative post. The ESS battery cable was a bit thinner than the same for the Main battery, just enough to notice. Is the opposite now true?

Yeah the thinner cable is the aux but it is connected to the black smart controller thing now. It has the plate for both connections. So now you have to remove both negative wires and reconnect the main negative to the smart controller. And if you have a winch theres very little room yo plig your negative winch wire now, and the nut is alao undersized.

 

[Heimkehr]

Yeah the thinner cable is the aux but it is connected to the black smart controller thing now. So now you have to remove both negative wires and reconnect the main negative to the smart controller.

Yes, that's identical to how my '21 was built. When I disconnected the ESS Neg cable to isolate the related battery, the Neg cable for the main battery was reconnected to the related battery post via the Intelligent Battery Sensor.

As described, I'm not perceiving any wiring swap between model years here. That's probably a good thing.

 

[entropy]

Yes, that's identical to how my '21 was built. When I disconnected the ESS Neg cable to isolate the related battery, the Neg cable for the main battery was reconnected to the related battery post via the Intelligent Battery Sensor.

As described, I'm not perceiving any wiring swap between model years here. That's probably a good thing.

Maybe I was stuck on pre 2021 models then

 

[AndySpill]

This is what I did in my 2019. I isolated the aux and kept it as a backup battery. But I no longer recommend this to people because of a couple reasons:

1) warranty. If theyre still under the short battery warranty window, it is best to leave the system alone.

I definitely see your point about, under warranty, keeping things as stock. I've read about people doing the bypass and then subjecting their Aux to periodic charging such that when they return to the dealer they can put things back factory and a charged Aux won't cannibalize the main battery.

2) the 2025 models, at least mine, swapped the negative wire connections. Meaning if you follow the directions posted here to isolate the aux you can end up unplugging the main negative. People can mess up. For example. If you then plug a battery charger to the unplluged negative and positive terminal you can end up frying something.

I do recall reading about a cable swap. https://www.jlwranglerforums.com/forum/threads/ess-battery-cable-change.86624/ This is why I tend to ask people to identify the cable on the main battery's negative post that leads to the body ground, whichever it is, and whichever model year of dual AGM battery JL is being modified, and leave that cable alone, the other factory cable being the one that connects to the Aux's negative terminal.

It's news to me that hooking a battery charger up to the positive terminal (I presume of the main battery as it's the only one visible) and the loose cable would anything but charge the Aux battery. Perhaps too high amperage could cause problems here.

My 2025 had an unrelated electricsl issue and when I was talking to my dealers service advisor they asked if I tried isolating the aux. Told me they see jeeps dailys with fried electronics cause people try messing with the ESS.

It's by no means unheard of that people have blown the high amp fuse array not being careful to tape up that loose cable before it comes into contact with metal.

If done correctly. Isolating the aux is the best you can do I agree. And you also end up with a backup starter battery as a plus. But people fuck up all the time, and the easiest for most is to simply swap both. A good pair should last a long time if ESS is deactivated.

It's true that what we tend to hear of on the forum is problems. And while an Aux battery going sideways and taking out the main battery with it is a common theme here, what isn't a common theme on the forum are the countless people who run dual batteries without much incident, who then don't find need to post on the forum to say, "hey guys, just checking in, my dual batteries are just fine."

 

[tk1700]

I mentioned doing the aux battery delete, She wants me to replace the aux battery, I'm suggesting both. I can have the main battery load tested at work.
Thank you all for your input.

You can replace the main battery only, do the aux disconnect (disconnect neg cable, pull fuse 42) and the ESS will continue to function. All power for ESS events will be provided by the main battery. Between 2 JL's I have a combined 5 years of running them like this without problems. For 95% of this time a Taser has been installed with the ESS button set to OFF.

 

[wolfdog]

I do not believe the aux battery has anything to do with remote start! My 2018 JLU ESS stopped working for 1 year, remote start continued working! Disconnected aux by undoing neg connect, remote start still good!! Replaced main battery 6 months later replaced main never have used aux battery since remote start good!!

Aux battery nothing to do with remote start!?

Go Jeep!!!

 

[entropy]

I definitely see your point about, under warranty, keeping things as stock. I've read about people doing the bypass and then subjecting their Aux to periodic charging such that when they return to the dealer they can put things back factory and a charged Aux won't cannibalize the main battery.



I do recall reading about a cable swap. https://www.jlwranglerforums.com/forum/threads/ess-battery-cable-change.86624/ This is why I tend to ask people to identify the cable on the main battery's negative post that leads to the body ground, whichever it is, and whichever model year of dual AGM battery JL is being modified, and leave that cable alone, the other factory cable being the one that connects to the Aux's negative terminal.

It's news to me that hooking a battery charger up to the positive terminal (I presume of the main battery as it's the only one visible) and the loose cable would anything but charge the Aux battery. Perhaps too high amperage could cause problems here.


It's by no means unheard of that people have blown the high amp fuse array not being careful to tape up that loose cable before it comes into contact with metal.


It's true that what we tend to hear of on the forum is problems. And while an Aux battery going sideways and taking out the main battery with it is a common theme here, what isn't a common theme on the forum are the countless people who run dual batteries without much incident, who then don't find need to post on the forum to say, "hey guys, just checking in, my dual batteries are just fine."

If you hook positive to the main battery and negative to the negative cable it will send bursts of high voltage current to the jeep and it can damage voltage sensitive electricsl components.

 

[AndySpill]

If you hook positive to the main battery and negative to the negative cable it will send bursts of high voltage current to the jeep and it can damage voltage sensitive electricsl components.

Ok. News to me.

My inclination would be that, based on Jerry's @Jebiruph's diagram below, that if you hook a device like a load tester to the main battery's positive terminal, and the exposed end of the disconnected cable between the Aux battery's negative post and the main battery's negative post, that you disconnected at the main battery's negative post, that you would load test the Aux battery in isolation, effecting no damage to the vehicle.

This too would be a way to hook up a charger to charge that Aux battery alone.

Now, if some short of a high amount of current followed this route, sure damage is a possibility, but such current can't effect damage in places where a complete circuit is not formed, right? And the only complete circuit I describe here is isolated to traveling thru the Aux battery that does not make its way to the body ground as the cable appearing below on the left side of the main battery's negative terminal is dangling in mid air, and it is only thru this cable's connection at the main battery's negative terminal that a circuit to the body ground would be formed.

Maybe I am missing something. Maybe the electronic components you cite ground themselves to the body and close a circuit that way.

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