DIY How-to: Take the Aux Battery Offline

[Lunentucker]

More on whether or not you'll begin to see signs.

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[Gezer]

I guess I should play the lottery. I must have good luck. My 2020 will be 4 years the end of august with the original batteries. I should also be looking at replacement. Does anybody recommend paying the xtra cash for brands like optima etc. I tried lithium in my Road King and lasted one year and it gave out and swelled so much it looked ready to pop. Thanks for any recommendations.

 

[Lunentucker]

I guess I should play the lottery. I must have good luck. My 2020 will be 4 years the end of august with the original batteries. I should also be looking at replacement. Does anybody recommend paying the xtra cash for brands like optima etc. I tried lithium in my Road King and lasted one year and it gave out and swelled so much it looked ready to pop. Thanks for any recommendations.

I don't think your NC summers or mine in VA are conducive to using the current lithium technology.
Is your JT garaged? I think that plays a role in the battery life of my vehicles.

When I researched some months ago, I found that most of the car batteries in the world are made by a few companies. Perhaps the individual brands have their own technologies and engineering that they use for blueprints?

Ultimately I'm looking for a battery with a good warranty and from a local source that I can get to should a problem arise.
I don't want to have to mail my defective battery anywhere.
So NAPA, Interstate, O'Reilly, Advance Auto... Whoever's fairly close by. Then just choose the better line at an appropriate rating.
If you need more power they do say a larger capacity and larger dimensionally 94R will fit.

 

[Whitewilly1le]

so really, is there any reason not to do this? Seems like a preventative no brainer.

 

[Lunentucker]

so really, is there any reason not to do this? Seems like a preventative no brainer.

The only downside would be if you're still under warranty and have an electrical or electronics issue, and the dealership sees what you did. You can bet that they'll try to exploit it to deny a claim.
The best thing to do there would be to undo the changes - about five minutes work, and then charge the system prior to taking it in for service.

 

[jebiruph]

The ESS system is easily deactivated with the removal of the F42 fuse. No further programming or tricks are needed. If I press the dash button the light on the button comes on. That's it. It's already off.

Removing the F42 fuse does not deactivate the ESS system, it just prevents the system from separating the batteries from each other.

For those waiting for the aux battery to go bad before disconnecting it, why? Disconnect it while it's still good and use it as an emergency backup in case the main battery goes dead.

 

[Lunentucker]

Removing the F42 fuse does not deactivate the ESS system, it just prevents the system from separating the batteries from each other.

For those waiting for the aux battery to go bad before disconnecting it, why? Disconnect it while it's still good and use it as an emergency backup in case the main battery goes dead.

I couldn't get mine to come on yesterday, despite repeated attempts with engine fully warmed up, city like stops, and no AC. Maybe it will later, but it sure acts like it's gone.

 

[jebiruph]

I couldn't get mine to come on yesterday, despite repeated attempts with engine fully warmed up, city like stops, and no AC. Maybe it will later, but it sure acts like it's gone.

F42 supplies power to the relay that separates the batteries during an ESS event, isolating the aux battery to power the interior electronics and leaving the main battery to power the restart. With the fuse removed, the batteries stay connected during an ESS event with both batteries powering the interior electronics and the restart. What removing the fuse does is allow you to disconnect the aux battery and run only with the main battery without causing any errors.

 

[Jeeperjamie]

It's normally the large battery that goes bad rarely the small aux battery. Not saying the aux battery does or doesn't help drain the large battery but I have 75,000 miles on my aux battery at it's still working. Replaced the large battery at 54,000 miles. These things get misdiagnosed all the time and people end up replacing both batteries or the small battery when the large battery is the bad one. Good video for someone considering this though but I'd prefer to keep the system the way it was designed.

 

[Maximus Gladius]

I have a trickle AGM battery tender installed and once every 4-6 days I do a 12v load test to see where the numbers are. Once the v hits 12.4 I plug it in over night and usually see upper 12 to low 13v. If I load check every morning, I see a drop of .10v.

I don’t do long drives every day so I know I’m not getting a proper charge. Thanks for your video!

 

[@californiajeeping]

Easier method.

Simply remove the aux and run the ground to chassis ground. the + undo the tape and loom so it reaches to the + lead on the main battery. I installed a odyssey slightly larger 96r on my diesel in place of the standard battery.

My voltage rarely drops below 14v now even with a large stereo. My ESS works as intended if wanted.

 

[ShadowsPapa]

The only difference here compared to some of the DIYs Jerry has done is the slide show....... otherwise, it's been hashed to death in dozens of threads and posts.
It truly IS simple. I mean SIMPLE. It's not rocket science and doesn't take over a 10th grade education.

Power simply can't flow without a full circular path - cut that path at any point and the circuit is dead. Disconnect either battery terminal and the circuit is dead, "power" can't "flow".

How long can we expect the auxiliary battery to last before it fails. I have the start/stop disabled using a tazer so I’m hoping the aux battery last longer.

Again, in dozens of posts all over the place - it doesn't matter.
Also - there's no such rule as "aux takes out main" - that's bull crap. If it was true why are so many 4xe owners replacing their 12v battery? There IS NO aux battery!
We've shown over and over that the main can be the first to fail, or the aux, or both together, If one fails first - it would have to fail as a short to kill the other battery so odds are against one killing the other. Look at the many members who have had just one or the other fail - replaced that battery, and moved on.
Disabling ESS doesn't make either battery not fail catastrophically. What happens when a battery is cycled over and over is a loss of long-term capacity. With AGM it supposedly takes longer.
What kills jeep batteries (aside from them being less than high quality) is how the vehicle is driven - or not driven (worse)
If it's only short drives, the batteries never get fully charged. That means owners are helping to kill batteries.

OK this is a rant but honestly two years of life for a battery that is essentially inaccessible is ridiculous. And the fact that you don't know when it is failing makes it all the worst.

Aux battery isn't that bad to get to through the wheel well. There's youtube videos out there showing that you don't even need to take things as far apart as some do.
I got 2.5 years out of my 2020 batteries only driving it mostly shorter runs and sometimes sitting 2, 3 or 4 days at a time. I traded it in still working.
An observant person can tell when batteries are going south if they watch the volt meter now and then.

If you pay attention to your truck, you will know when it's having an issue with either of the batteries. The truck does a test every fresh start. It then will exhibit signs or warnings of a battery issue, such as ESS never engaging saying 'not ready - battery charging' or showing warnings about AUX switches not being available due to battery levels. Problem is most people are just ignoring these things and then act surprised when it finally gives out.

Totally agree though that the lifespan of the original batteries is crap. But if you get a good battery in there, the system works just fine.

Yes- this ^^^^^
You may not recognize the problem coming up - but the tells are there.

I waited long enough to replace the pony battery the main battery was damaged. Still no indication of a problem from the system diagnostics.

Diagnostics don't do the job when the big battery camouflages the failing pony battery. Wish that they did, but provably they don't.

What generally happens is that because they are tied together in parallel - both have actually gone bad, average lifespan and all. People say one ruined the other, but unless one shorts, it's not likely. I've enough time in electronics to be able to say - if one goes replace both because it's been through the exact same charging and discharge cycles, the same voltages charging (or not charging due to lack of long drives) and so on.
Example - 6 CAD stations at work. All bought and put into service the same week. A monitor went bad on one. We replaced it. About a week later, a monitor went bad on another. Then a couple of days later, another. In a bit over 3 weeks all 6 monitors had gone bad.
We had the same thing happen with hard drives in one department when I worked for the state. They all failed within a short timeframe.
One can fail and the other last a few more months, but since they both have the same history, it's just plain smart to replace them both. They've had the same rough life.
And yes - there's no "system diagnostics" that says "hey, your battery is bad!" but there are signs. ESS battery charging, aux switches not working, changes in the voltage reading patterns. But one must pay attention.
Batteries can simply "die". It does happen, but very often there are tells.

This should be made a Sticky!

Along with Jerry's posts and some others...........
The difference is this is a slideshow.

The ESS system is easily deactivated with the removal of the F42 fuse.

That simply keeps the system from doing a startup battery check on the aux battery. ESS will still function for about half a dozen cycles before it stops working because the system decides something is wrong.
Pulling the fuse only prevents an error when it opens the PCR to test the aux battery.
Nothing keeps ESS from operating since it still believes there's a battery there because the PCR stays closed providing voltage from the main battery to N1.

https://www.jeepgladiatorforum.com/forum/threads/jumperless-aux-battery-pcr-bypass.59836/

 

[ShadowsPapa]

Easier method.

Simply remove the aux and run the ground to chassis ground. the + undo the tape and loom so it reaches to the + lead on the main battery. I installed a odyssey slightly larger 96r on my diesel in place of the standard battery.

My voltage rarely drops below 14v now even with a large stereo. My ESS works as intended if wanted.

What's easier than pulling 1 fuse and pulling one end of one cable loose? Does the same thing because the PCR is staying closed keeping the main battery connected to N1.
ESS will still work. You can take the aux battery out later if desired (or keep it charged up as a spare/booster)

This slideshow makes it so bloody easy even a kid could do it.

 

[ShadowsPapa]

Sad that a really super-simple., to the point - step 1, step 2 and so on pictorial that should be left alone just as it was always devolves into a "yeah, but" or a "I hate xyz" thing or the spreading of conjecture or opinion based on what's out there on the internet and youtube.

This really should be paired up with Jerry's (he explains why and what it does) and trimmed of all comments and locked down to just Lunentucker's and maybe Jerry's info and nothing more.

What he's done here is taken the text with pictures version from the Wrangler side - which Jerry made and brought over here and made it very simple. Can't get any easier than "pull fuse, remove cable" but it's watered down with some other stuff that's just repeats of internet lore.

MAYBE Jay or a mod will trim the thread down to the first post and sticky and lock it?

Jerry's thread turned into 8 pages as well.

Do it or don't do it. IT's also that simple. IF you have no problems and aren't worried about the stuff you read out there, leave it alone. If you are paranoid about the evil aux battery, pull the F42 fuse and disconnect the aux battery negative cable at the top of the IBS and be done.
ESS will still function - for a few times, about 6 or so per big button start.

"The system" thinks it's opened the PCR, it sent the open PCR signal so it could check the aux battery. Believing it did so, it checks voltage - hey, amazing, same as the main battery, it's up and good to go. Thus no error is generated.
Disconnecting the negative aux cable from the top of the IBS takes the aux battery off line, nothing more, nothing less. ESS will still function because the PCM believes it opened the PCR and tested the battery voltage. It sent the signal to open it, it checked voltage and found it to be fine, so ESS will work. ESS doesn't rely on that PCR opening. It could be stuck closed and it would still work.

This is what Jerry said -

F42 PCR CTRL FEED (ESS)*. Removing this fuse defeats the cold start aux battery test and allows the aux battery to be disconnected without generating any errors.

 

[rwu355]

My original batteries only lasted about a year and 3 months.

I got about 2-1/2 years out of mine, then started getting odd messages about Aux switches being out of service at start up. Replaced both batteries all us well Now. I have the Auto-Stop/Start disabled so it doesn’t drain the setup. By the time I hit 3 years in October I’ll probably have 52-53,000 miles So it does get driven.

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