Both batteries replaced at 22k mi

[entropy]

Most of the time, yes. But not during engine starts. Starting the engine without imposing a brownout to the electronics is the entire reason why the Aux battery exists.

In a cold start the batteries are isolated and the Main starts the engine while the Aux supports the basic electronics.
In a warm start (ESS) the batteries are isolated and the Aux starts the engine while the main supports the electronics, HVAC, Radio and everything else that may be in use.

At all other times (including when parked) the batteries are linked so they can be recharged and share the burden of the JL's parked parasitic draw.

I still don't get what is so important about keeping the AUX battery.... if you turn off ESS then you're golden, and you have an AUX battery ready to be plugged back as an emergency backup. All you are giving up is ESS and a dozen potential headaches. I've been running with just the main for well over a year with 0 issues.

My Camry has one battery and no headaches.

Sponsored

 

[Reinen]

I still don't get what is so important about keeping the AUX battery.... if you turn off ESS then you're golden, and you have an AUX battery ready to be plugged back as an emergency backup. All you are giving up is ESS and a dozen potential headaches. I've been running with just the main for well over a year with 0 issues.

My Camry has one battery and no headaches.

Aux is not exclusively used by ESS. It keeps the basic vehicle electronics happily juiced when the main battery is dumping power to the starter.

Jeeps are well known for having owner installed accessories. It's pretty much expected. These are often wired directly to the battery DIY style. So who knows what else the main battery needs to power besides the starter and how low volts/amps will drop in the process. We all know JL electronics do weird things at low voltage/amps and that's the last thing you want while you're trying to crank start your cold engine. The Aux battery eliminates that possibility by insuring the electronics has strong clean power.

It's a classic engineer CYA move. If the JL won't start because its electronics glitch out due to power hungry accessories running during the cold start, people will blame the Jeep not the accessories. If accessories brown out during cold starts but the Jeep starts up just fine, people will blame the accessories not the Jeep.

Nobody accessorizes a Camry and it only goes where Roadside Assistance is. Single battery is good enough for that.

 

[jludave]

Is it the same procedure for the 2.0 as the 3.6?

Yes.

If so is there a link or anything for instructions on what to do for the bypass? I

https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/

 

[entropy]

Aux is not exclusively used by ESS. It keeps the basic vehicle electronics happily juiced when the main battery is dumping power to the starter.

Jeeps are well known for having owner installed accessories. It's pretty much expected. These are often wired directly to the battery DIY style. So who knows what else the main battery needs to power besides the starter and how low volts/amps will drop in the process. We all know JL electronics do weird things at low voltage/amps and that's the last thing you want while you're trying to crank start your cold engine. The Aux battery eliminates that possibility by insuring the electronics has strong clean power.

It's a classic engineer CYA move. If the JL won't start because its electronics glitch out due to power hungry accessories running during the cold start, people will blame the Jeep not the accessories. If accessories brown out during cold starts but the Jeep starts up just fine, people will blame the accessories not the Jeep.

Nobody accessorizes a Camry and it only goes where Roadside Assistance is. Single battery is good enough for that.

Well it seems my main has plenty juice then because I have 0 issues running with the aux on isolation mode. Over a year and counting.

 

[Reinen]

Well it seems my main has plenty juice then because I have 0 issues running with the aux on isolation mode. Over a year and counting.

The problem will reveal itself when the Main dies. Critical things will fail first increasing the likelihood of finding yourself stranded.

 

[SmoothOperation156]

The problem will reveal itself when the Main dies. Critical things will fail first increasing the likelihood of finding yourself stranded.

Explain it to me like I’m 12 LOL.
I’m confused on the root problem here, I don’t really have knowledge on electrical, genuinely trying to understand the problem if there’s any info you or anyone else can give on how the AUX correlates to this and why bypassing it alleviates the issue.

 

[mwilk012]

Explain it to me like I’m 12 LOL.
I’m confused on the root problem here, I don’t really have knowledge on electrical, genuinely trying to understand the problem if there’s any info you or anyone else can give on how the AUX correlates to this and why bypassing it alleviates the issue.

It’s no different from any other car, when your battery goes bad your vehicle won’t work right. It can manifest as spurious communication faults and other gibberish or just the plain old no start no crank.

 

[SmoothOperation156]

It’s no different from any other car, when your battery goes bad your vehicle won’t work right. It can manifest as spurious communication faults and other gibberish or just the plain old no start no crank.

Right, but how does the addition of the AUX battery make things worse to the point both of them have to get replaced in under 25k miles?

 

[mwilk012]

Right, but how does the addition of the AUX battery make things worse to the point both of them have to get replaced in under 25k miles?

Mopar batteries are junk

 

[Greendezl]

I replaced my main battery with an Odyssey and deleted the Aux junk.

 

[jludave]

Right, but how does the addition of the AUX battery make things worse to the point both of them have to get replaced in under 25k miles?

The main and aux are connected in parallel. One goes bad, so does the other. What affects one, affects the other.

Plus, as already mentioned, the OEM batteries are crap.

 

[speedymart]

Hi all,

I have a '21 JLUR I purchased less than 6 months ago and took it to the dealer for an oil change and a couple of items I wanted to have checked out under warranty One of the rear tail lights holding moisture, and my stop/start system never engaging with the service stop/start sometimes appearing on that page. I know stop/start is a controversial topic but I'd like to have all of the features I paid for and I figured I'd have the dealer take a look at it.

Tail light was an easy fix, they replaced it for free. Probably a micro-fracture in the housing somewhere.

I know the auxiliary battery on these JL's has had some issues so was expecting them to replace just the auxillary battery after running their battery tests. HOWEVER, they actually replaced BOTH batteries under warranty, after they BOTH failed their battery tests. I hadn't noticed any electronic issues or power issues related to the main battery so was suprised they decided to replace both batteries.

Again, all under warranty so at no cost to me. Just wanted to forward this along to any other JL owners who have any issues with their auxiliary battery, I don't know if replacing both of the batteries is a common fix or if I was a special case, but just found it interesting enough to share.

The way most techs replace the aux battery at this point requires the primary battery to be removed. Absolutely zero reason to not just replace it while it's out to get the additional 0.5 hours flag time it pays. 99% of techs "failing" your battery under warranty aren't testing it and just replacing it. Warranty time doesn't pay enough to let a test run for 1-3 hours. Welcome to the reality of flat rate. Enjoy the new batteries!


And yeah, mopar batteries are complete junk. The aux batteries literally have a made in china label on them now. Delete your aux battery and stop using stop/start, the amount of fuel you'll save over the lifetime of the vehicle will be wiped out by a singular aux battery failure outside of warranty.

 

[STW]

Hi all,

I have a '21 JLUR I purchased less than 6 months ago and took it to the dealer for an oil change and a couple of items I wanted to have checked out under warranty One of the rear tail lights holding moisture, and my stop/start system never engaging with the service stop/start sometimes appearing on that page. I know stop/start is a controversial topic but I'd like to have all of the features I paid for and I figured I'd have the dealer take a look at it.

Tail light was an easy fix, they replaced it for free. Probably a micro-fracture in the housing somewhere.

I know the auxiliary battery on these JL's has had some issues so was expecting them to replace just the auxillary battery after running their battery tests. HOWEVER, they actually replaced BOTH batteries under warranty, after they BOTH failed their battery tests. I hadn't noticed any electronic issues or power issues related to the main battery so was surprised they decided to replace both batteries.

Again, all under warranty so at no cost to me. Just wanted to forward this along to any other JL owners who have any issues with their auxiliary battery, I don't know if replacing both of the batteries is a common fix or if I was a special case, but just found it interesting enough to share.

like the others said, it's not the aux that's the problem (and not Start/Stop that's the problem either, because it works fine with eTorque). It's the way Jeep implemented the Main/Aux system, wiring them in parallel with the result they parasitically drain and damage each other when there is not enough charging time. This easily happens for people who do lots of short drives.

There are a few fixes for this, and you should choose one or more of these now that you have to new batteries: 1) regular long drives so the alternator has enough time to keep them both topped up. 2) keep the main on a top-up charger when it's parked in the garage (can top up the Aux this way too). Do a jumperless bypass of the Aux, so they are no longer wired in parallel (this is what I did as part one of my fix).

The good news is you have two new batteries. The bad news is they are still at risk of draining each other over time.

 

[SmoothOperation156]

like the others said, it's not the aux that's the problem (and not Start/Stop that's the problem either, because it works fine with eTorque). It's the way Jeep implemented the Main/Aux system, wiring them in parallel with the result they parasitically drain and damage each other when there is not enough charging time. This easily happens for people who do lots of short drives.

There are a few fixes for this, and you should choose one or more of these now that you have to new batteries: 1) regular long drives so the alternator has enough time to keep them both topped up. 2) keep the main on a top-up charger when it's parked in the garage (can top up the Aux this way too). Do a jumperless bypass of the Aux, so they are no longer wired in parallel (this is what I did as part one of my fix).

The good news is you have two new batteries. The bad news is they are still at risk of draining each other over time.

Clear and concise thank you very much!

 

[Rhinebeck01]

The way most techs replace the aux battery at this point requires the primary battery to be removed. Absolutely zero reason to not just replace it while it's out to get the additional 0.5 hours flag time it pays. 99% of techs "failing" your battery under warranty aren't testing it and just replacing it. Warranty time doesn't pay enough to let a test run for 1-3 hours. Welcome to the reality of flat rate. Enjoy the new batteries!


And yeah, mopar batteries are complete junk. The aux batteries literally have a made in china label on them now. Delete your aux battery and stop using stop/start, the amount of fuel you'll save over the lifetime of the vehicle will be wiped out by a singular aux battery failure outside of warranty.

@speedymart

You say...
"The way most techs replace the aux battery at this point requires the primary battery to be removed. "

I'm unsure why you think this.. Techs more often then not do a fender liner peel which is the way Stellantis recommends they do the deed. This requires cutting a few plastic rivets and peeling back the fender liner a bit.. IF not a peel that cut two rivets and bungee cord the liner back a bit and do the deed.

NO, they do not dismantle the PDC even though the Aux on a 3.6 is under there... NO, the aux battery is not under the Main battery.

Also, Tech has to provide test result(s) to Stellantis if they want dealership to be reimbursed for bad battery(s).

I am not being confrontational in regard to my comments here... but rather just wanting to get correct info to other's.

.

Sponsored