My thoughts on the auxiliary battery

[Andy29847]

If

The main battery can handle it all. The aux battery will power computers , blower fan radio until it is detected to be at a low state. Then you would get the battery charging message. Without the aux, you would have the possibility of a no start due to consuming your batteries power.

The Jeep black boxes will continue to sample the available battery power regardless if there is one battery or 2 batteries. In the case of one battery, if the voltage thresholds aren’t met, then the stop start will not function. The big difference is that when/if this happens, you will not have to figure out which battery is causing your problem.

Also, with one battery, the Jeep voltmeter readings become more useful.

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[Lost1wing]

If


The Jeep black boxes will continue to sample the available battery power regardless if there is one battery or 2 batteries. In the case of one battery, if the voltage thresholds aren’t met, then the stop start will not function. The big difference is that when/if this happens, you will not have to figure out which battery is causing your problem.

Also, with one battery, the Jeep voltmeter readings become more useful.

Good point. If you have your battery voltage displayed during a start stop, your aux battery is what is being displayed. Not sure on that, but that is what I suspect.

 

[Andy29847]

Good point. If you have your battery voltage displayed during a start stop, your aux battery is what is being displayed. Not sure on that, but that is what I suspect.

I think it is ShadowsPapa who has done the testing using voltmeters on both batteries. He says the voltage displayed during a stop start is the aux battery voltage. My own testing confirmed this to my satisfaction. Of course, when there is just one battery, the voltmeter is reading that ONE battery all the time. I'm convinced that even with the aux battery deleted, all the Jeep's systems and sensors still work as designed.

 

[The Sigma]

Disconnecting the aux negative, and pulling f42 only prevents the pcr from isolating the two batteries during the start up test. ESS is still active, using only the main battery. The only benefit of this would be if your aux battery was bad and dragging down your main. Potential problem with doing this is the computers seeing the voltage drop during a start stop event. If you select start stop to be off, (doesn't matter how you do it), you won't have that risk during a stop start event.

This was the point I was at. For reference (if that contributes anything) is that my Gladiator is a 2020 that has the original batteries in it. Seeing the consistent high voltage, taking the aux out of the equation by disconnecting the negative and pulling #42, and then seeing the voltage drop to what I thought was a "normal" range led me to think that it was my aux which was dead or dying and I happened to catch it before my main was affected as well - i.e. I wasn't stuck with a 2 battery replacement. I do have a Tazer which has kept the ESS off ever since I've owned my vehicle.

 

[Andy29847]

Good point. If you have your battery voltage displayed during a start stop, your aux battery is what is being displayed. Not sure on that, but that is what I suspect.

I had my first bit of battery trouble in OCT 2022. It took several trips to the dealer over 6 months to remedy (2 new batteries) my situation. Most of what I know about the battery systems on our Jeeps came from study here on this forum during my trouble period. Here is a post in the thread where the issue of what the voltmeter is displaying during a stop/start event was settled for me.

https://www.jeepgladiatorforum.com/...tage-truck-off-and-at-rest.56213/post-1073502

This is a long thread, maybe best read from back to front. Reading from the front you find a lot of testing and guessing and a variety of conclusions. Near the end, most of the questions have been answered.

 

[chorky]

ry can handle it all. The aux battery will power computers , blower fan radio until it is detected to be at a low state. Then you would get the battery charging message. Without the aux, you would have the possibility of a no start due to consuming your batt

I think it would be highly unlikely to have a no start from a ESS event because of a battery drain. One of the primary purposes of the system as a whole is to not drop below a particular voltage threshold, so if it sees low voltage from just one battery with the aux removed it will restart the engine. At least that's my understanding.

I am curious what electronics are so sensitive that a brief voltage drop due to cranking the starter will cause damage. If that's the case then wouldn't the same worry exist upon initial cold start? Or starting at any time? I have looked over the ESS system drawings so many times that, short of having a EVTM it doesn't seem to make all that much of a difference in the first place.

 

[Glad Jeeper]

This thread is answering more of my questions. Since getting my JTM in 2021. I have read plenty of threads like this that would be a major concern especially for those of us that overland and can be many miles away from any type of service center. It is habit that I turn of the Start/stop function every time I start the truck up, I am hoping this will extend or save me from battery issues in the future.
I am questioning changing batteries soon or waiting till issues start showing up. Of all the vehicles I have ever owned I can only remember 1 that I had to purchase new batteries and it was 12 years old.
Are there any or alot of JT's that dont have issues?

 

[Lost1wing]

I think it would be highly unlikely to have a no start from a ESS event because of a battery drain. One of the primary purposes of the system as a whole is to not drop below a particular voltage threshold, so if it sees low voltage from just one battery with the aux removed it will restart the engine. At least that's my understanding.

I am curious what electronics are so sensitive that a brief voltage drop due to cranking the starter will cause damage. If that's the case then wouldn't the same worry exist upon initial cold start? Or starting at any time? I have looked over the ESS system drawings so many times that, short of having a EVTM it doesn't seem to make all that much of a difference in the first place.

In the past, airbag, ABS would typically trigger faults during an engine start due to the voltage drop. U codes also also pop up ( communication errors) It may not cause permanent damage bit repeated over and over is asking for trouble. Relying on one battery ( aux deleted f42 pulled) is not the design of the system. I can see a good main battery holding up. Eventually, it will degrade and cause issues.

 

[Lost1wing]

I had my first bit of battery trouble in OCT 2022. It took several trips to the dealer over 6 months to remedy (2 new batteries) my situation. Most of what I know about the battery systems on our Jeeps came from study here on this forum during my trouble period. Here is a post in the thread where the issue of what the voltmeter is displaying during a stop/start event was settled for me.

https://www.jeepgladiatorforum.com/...tage-truck-off-and-at-rest.56213/post-1073502

This is a long thread, maybe best read from back to front. Reading from the front you find a lot of testing and guessing and a variety of conclusions. Near the end, most of the questions have been answered.

I need a nap now that I have read all of that. I did read some of it before. I was into some of the testing and was testing mine back then.

 

[chorky]

In the past, airbag, ABS would typically trigger faults during an engine start due to the voltage drop. U codes also also pop up ( communication errors) It may not cause permanent damage bit repeated over and over is asking for trouble. Relying on one battery ( aux deleted f42 pulled) is not the design of the system. I can see a good main battery holding up. Eventually, it will degrade and cause issues.

Well we definitely know without a doubt that a bad aux or main battery will pull down the other and making some really messy problems. I fail to see how that situation would be any better than relying on one battery and it slowly dying. Either way, unless ESS is turned off, a person will see Christmas lights.

I could understand how, if keeping the factory aux battery, it somehow protects all those circuits, doesn't throw codes or lights, and truly stabilizes voltages. But that's just not the case..... And that really can't be the case unless said circuits are totally isolated and running purely on the aux battery. But in that event, when the aux eventually does go bad it will still cause those systems to freak out. The only way to prevent any of this, that I can see, is be presumptive and replace batteries every 2-3 years no matter if they are good or bad - just to stay ahead of the game.

 

[Lost1wing]

Well we definitely know without a doubt that a bad aux or main battery will pull down the other and making some really messy problems. I fail to see how that situation would be any better than relying on one battery and it slowly dying. Either way, unless ESS is turned off, a person will see Christmas lights.

I could understand how, if keeping the factory aux battery, it somehow protects all those circuits, doesn't throw codes or lights, and truly stabilizes voltages. But that's just not the case..... And that really can't be the case unless said circuits are totally isolated and running purely on the aux battery. But in that event, when the aux eventually does go bad it will still cause those systems to freak out. The only way to prevent any of this, that I can see, is be presumptive and replace batteries every 2-3 years no matter if they are good or bad - just to stay ahead of the game.

My though there is the reason I look at the ESS page. If I see Stop start Ready right after warm up, I take that as a good sign. If I see Battery charging for an extended time, it is time to investigate. Both times that I saw the battery charging message stay on for most of my drive, I put the charger on it. The second time I also reset the IBS and it has been good since that time.

 

[chorky]

My though there is the reason I look at the ESS page. If I see Stop start Ready right after warm up, I take that as a good sign. If I see Battery charging for an extended time, it is time to investigate. Both times that I saw the battery charging message stay on for most of my drive, I put the charger on it. The second time I also reset the IBS and it has been good since that time.

Yeah thats a really good point. But I thought we determined from past discussions via Shadow that the IBS doesn't even look at the aux. For me it hasn't been much help. When I first got my JT it would take about a 45 minute drive for the ESS to be ready - mostly due to cold outside temps. In the winter it almost always charges 14.5-15v. Only on long drives, like longer than 2.5 hours, will it slowly drop down, and even then still stays above 13 most the time. In the summer is when the voltage drops - it's purely just a cold temperature thing for me. Heck in the winter, with a reset IBS and good batteries it took nearly an hour every single time for the 'ESS ready" message to come up. I guess I just dont see the benefits. Maybe I'm missing something though. But it kinda sounds like, in that situation, the only purpose of monitoring the ESS status is to be able to tell if one of your batteries is starting to go bad?

 

[Mr._Bill]

The life expectancy of batteries in the JT is about three years. The high heat under the hood and the parasitic draw combine to shorten the battery life. The Aux battery can last longer, just due to its location.

A constant high system voltage (14+) shows the batteries are needing and being charged. This doesn't mean that there is a problem, or failing battery, only that the truck is not driven enough to keep the batteries charged. However, it can show there is a problem if the truck is driven regularly or the batteries are older.

The clear warning sign is the pop-up messages that ESS or Aux switches are unavailable. Separately charging both batteries and resetting the IBS will buy some time, depending on the batteries condition, but this is the warning that replacement is in the near future. If you ignore this and just keep going, you will eventually be in a no-start situation.

 

[chorky]

The life expectancy of batteries in the JT is about three years. The high heat under the hood and the parasitic draw combine to shorten the battery life. The Aux battery can last longer, just due to its location.

A constant high system voltage (14+) shows the batteries are needing and being charged. This doesn't mean that there is a problem, or failing battery, only that the truck is not driven enough to keep the batteries charged. However, it can show there is a problem if the truck is driven regularly or the batteries are older.

The clear warning sign is the pop-up messages that ESS or Aux switches are unavailable. Separately charging both batteries and resetting the IBS will buy some time, depending on the batteries condition, but this is the warning that replacement is in the near future. If you ignore this and just keep going, you will eventually be in a no-start situation.

Cold temperatures also trigger high voltage charging. Even vehicles driven daily.

 

[chorky]

This situation is also one of the reasons I went the route of the Genesis system and stuck with AGM house batteries. Self jump starting. Because I and many I know have been in the middle of nowhere with a no-start battery issue. Just throwing that out there

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