AUX battery delete/bypass - Which method is proper?

[THAW]

So, prior to pulling the aux batt, if I pulled the battery cables off the main battery, everything still had power as if the two batts were in true parallel wiring, as opposed to relay based A/B switching. So that power had to be coming from the aux batt.

That behavior is expected. The PCR is normally closed, so the battery wiring would've been connected (i.e. not switched open) while you were tinkering.

I want to pull the F42 fuse and see if it behaves differently. Just as a test.

In your case, pulling fuse F42 shouldn't make a difference. That fuse allows the PCR to open, and your PCR apparently isn't opening. Removing the fuse would turn off a dash warning light - but you don't have one.

Have you checked fuse F42 to see if it's blown?

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[AndySpill]

....I decided to try not using the aux on my battery swap.

Hi Scott:

Would you please explain to me exactly what you mean by your decision to try to not use the aux battery?

I ask this because some owners falsely believe that such actions equate with, for example, pressing the ESS off button and not running such events--and in such circumstances--pardon me if I've insulted your intelligence, by no means is the ESS battery not still being used.

Do you mean to imply that you, as described by you below, electrically disconnected the Aux battery from the vehicle's electrical schematic and perhaps pulled Fuse 42?

So while I had the main battery out I decided to test out some of what I read and I pulled the aux and insulated both cable ends, and tucked them back in the aux batt compartment. Then put in the new main battery. I didn't strap the aux cables back to the terminals, and I didn't pull the ESS fuse, and I didn't install any jumpers.

I'm curious, is there an ESS off light illuminated in the dash: an "A" icon with a near circle around it and a slash through it? I'd expect this based on what you described. Understand please that I am NOT referring to the status of the ESS off button that you could press.

To elaborate, without an Aux battery connected I'd expect your 2021 to not crank on the first attempt after disconnecting the Aux battery but NOT Fuse 42 (keeping the fuse in place.) Then, I'd expect on subsequent cranks the vehicle to attempt to crank solely off the main battery, and if successful, illuminate this light I just talked about.

So far, everything seems normal. No warnings, voltages seem normal, and if I forget to push the ESS switch, it will do it's thing.

I'm hearing you say that there is no connected ESS battery, Fuse 42 is intact, and there is no jumper between N1 and N2 in the Power Distribtion Center (PDC) and despite this fact, if you don't turn ESS off, from time to time you will experience ESS events?

Been driving it like this for about 5 days and all seems well.

Two things I'm curious about. One is that the whole pull the F42 fuse seems to be often suggested advice. I decided to try this without pulling that fuse and it seems fine, so I never bothered to try it with the fuse pulled. I guess I don't understand why some folks need to do this, and why I don't?

Pulling Fuse 42 is often indicated advice in this circumstance because doing so prevents the Power Control Relay (PCR, not to be confused with the PDC, lots of acronyms, I know!) from ever being energized. The PCR is a normally closed relay. If you are not familiar with what this means, in plain speak, it means that when the PCR is not provided power (which is the case even with Fuse 42 intact at all times but an instant prior to cold cranking and during ESS events) the batteries, at least in the factory setup, are connected in parallel.

It's when this circuit is energized that the batteries are separated. This said, lets rediscuss the cold crank process. As mentioned, the vehicle attempts to separate the batteries for an instant but, unaware of this fact, cannot because the PCR can't be energized thanks to the fuse pull, and all calls for power to either battery are instead routed to all available batteries, of which only the main battery is typically still connected.

I too am at a loss to explain how with no ESS battery connected, and Fuse 42 intact, and no jumper between N1 and N2 in the PDC how you are experienced that which you describe.

The other thing is that I had come across a post (which I can't find now) where a guy claimed that the elimination of the aux battery damaged his charging system.

The above claim simply does not comport with what happens when a factory dual AGM battery JL experiences a disconnected Aux battery and Fuse 42 pull. All calls for power, and all power from the alternator silently go to and from solely the main battery.

The only thing I can think of here is maybe the guy had a main battery about to die, and decided to run ESS events with the one battery, which I don't recommend. Even then, I find this anecdote an odd one.

That really doesn't make any sense to me since the alternator shouldn't care if it's charging one or two batteries, especially if they are paralleled. It should just look like one big battery.

Scott: I don't mean to be pendantic and nit picky, except where not doing so interferes with understanding. I say this because the guy you described claimed to take the Aux battery out of the electrical schematic of the vehicle, right? This should be like like just one battery, not one big battery, the latter of which implying to me the two factory batteries connected in parallel.

Yet that same thread there were plenty of folks jumping on the aux batt delete as a bad and dangerous thing.

The Aux battery is not, I think, a dangerous thing. What I think is that for those who have made the decision to not run ESS events, its benefit to the vehicle is so far outweighed by the possibility of it crapping out before the main battery, and given its parallel connection to the main battery, possibly cannibalizing it. A bad Aux battery in parallel with the main could seek, unsuccessfully, to equalize its charge with the main battery, pulling its power, but be enable to take that power and put it into itself, leaving two compromised batteries. The AGM battery chemistry batteries of such JLs don't "like" being brought below a 20% state of charge as might happen in such cases.

I don't really follow their logic with that. Seems to me that charging a single main battery would be a lot easier on the charging system than constantly having to make up for charge loss from a failing aux battery?

Now you've lost me. Would not the simpler design you describe immediately above NOT be consistent with the claims of others you cite, and that confuse you, that this simpler design is less bad....better...good, making the two battery setup, at least for those who don't run ESS events...well...bad as others have descibed?

Anecdotally, so far I've seen no evidence of odd behavior, no warning lights, no voltage levels that cause concern. In fact my voltages have been better without the aux batt. With it, I was seeing as low as 12.2 after a cold morning start, up to 13.9-14.0. With the aux battery completely eliminated, my low voltage after a cold morning start was 12.6 and running charge is 13.9-14.0, typically running 12.8 ish going down the road once the batt was recharged.

I'd be curious as to what the group thinks

I do not know how, with the ESS battery disconnected as I believe you claim, but Fuse 42 intact and working, along with a PCR capable of being energized, and no N1 -N2 jumper, how your vehicle is getting tricked into thinking that there is an ESS battery, and NOT turning on the ESS off light in the dash I described earlier.

One of us, maybe me, has missed something or your vehicle is not operating as per spec. Please examine Fuse 42 to see if it is blown. Perhaps you are familiar. If not, and you own a multimeter, you can use it to establish if the Fuse conducts current as per this:

 

[Max Headroom]

Hi Scott:

Would you please explain to me exactly what you mean by your decision to try to not use the aux battery?

I ask this because some owners falsely believe that such actions equate with, for example, pressing the ESS off button and not running such events--and in such circumstances--pardon me if I've insulted your intelligence, by no means is the ESS battery not still being used.

Do you mean to imply that you, as described by you below, electrically disconnected the Aux battery from the vehicle's electrical schematic and perhaps pulled Fuse 42?



I'm curious, is there an ESS off light illuminated in the dash: an "A" icon with a near circle around it and a slash through it? I'd expect this based on what you described. Understand please that I am NOT referring to the status of the ESS off button that you could press.

To elaborate, without an Aux battery connected I'd expect your 2021 to not crank on the first attempt after disconnecting the Aux battery but NOT Fuse 42 (keeping the fuse in place.) Then, I'd expect on subsequent cranks the vehicle to attempt to crank solely off the main battery, and if successful, illuminate this light I just talked about.



I'm hearing you say that there is no connected ESS battery, Fuse 42 is intact, and there is no jumper between N1 and N2 in the Power Distribtion Center (PDC) and despite this fact, if you don't turn ESS off, from time to time you will experience ESS events?



Pulling Fuse 42 is often indicated advice in this circumstance because doing so prevents the Power Control Relay (PCR, not to be confused with the PDC, lots of acronyms, I know!) from ever being energized. The PCR is a normally closed relay. If you are not familiar with what this means, in plain speak, it means that when the PCR is not provided power (which is the case even with Fuse 42 intact at all times but an instant prior to cold cranking and during ESS events) the batteries, at least in the factory setup, are connected in parallel.

It's when this circuit is energized that the batteries are separated. This said, lets rediscuss the cold crank process. As mentioned, the vehicle attempts to separate the batteries for an instant but, unaware of this fact, cannot because the PCR can't be energized thanks to the fuse pull, and all calls for power to either battery are instead routed to all available batteries, of which only the main battery is typically still connected.

I too am at a loss to explain how with no ESS battery connected, and Fuse 42 intact, and no jumper between N1 and N2 in the PDC how you are experienced that which you describe.



The above claim simply does not comport with what happens when a factory dual AGM battery JL experiences a disconnected Aux battery and Fuse 42 pull. All calls for power, and all power from the alternator silently go to and from solely the main battery.

The only thing I can think of here is maybe the guy had a main battery about to die, and decided to run ESS events with the one battery, which I don't recommend. Even then, I find this anecdote an odd one.



Scott: I don't mean to be pendantic and nit picky, except where not doing so interferes with understanding. I say this because the guy you described claimed to take the Aux battery out of the electrical schematic of the vehicle, right? This should be like like just one battery, not one big battery, the latter of which implying to me the two factory batteries connected in parallel.


The Aux battery is not, I think, a dangerous thing. What I think is that for those who have made the decision to not run ESS events, its benefit to the vehicle is so far outweighed by the possibility of it crapping out before the main battery, and given its parallel connection to the main battery, possibly cannibalizing it. A bad Aux battery in parallel with the main could seek, unsuccessfully, to equalize its charge with the main battery, pulling its power, but be enable to take that power and put it into itself, leaving two compromised batteries. The AGM battery chemistry batteries of such JLs don't "like" being brought below a 20% state of charge as might happen in such cases.



Now you've lost me. Would not the simpler design you describe immediately above NOT be consistent with the claims of others you cite, and that confuse you, that this simpler design is less bad....better...good, making the two battery setup, at least for those who don't run ESS events...well...bad as others have descibed?



I do not know how, with the ESS battery disconnected as I believe you claim, but Fuse 42 intact and working, along with a PCR capable of being energized, and no N1 -N2 jumper, how your vehicle is getting tricked into thinking that there is an ESS battery, and NOT turning on the ESS off light in the dash I described earlier.

One of us, maybe me, has missed something or your vehicle is not operating as per spec. Please examine Fuse 42 to see if it is blown. Perhaps you are familiar. If not, and you own a multimeter, you can use it to establish if the Fuse conducts current as per this:

Now I looked to see if F42 is in the fuse block when I did this, which it is. But I didn't pull it and run a continuity check on it. Maybe it is blown. I will have to go check that.

 

[Max Headroom]

One of us, maybe me, has missed something or your vehicle is not operating as per spec. Please examine Fuse 42 to see if it is blown. Perhaps you are familiar. If not, and you own a multimeter, you can use it to establish if the Fuse conducts current as per this:

Ok, I can add more information.
The F42 fuse is good.

So why does the jeep behave the way I described earlier? The NC relay that separates the batteries was stuck closed.

The afternoon I removed the aux battery I zoned out pushing the 'no ESS button' and had an ESS event. Jeep shut down at a stop and restarted when I hit the ess button.

A day or so later, I had another unwanted/unplanned ess because I forgot the switch. This one also worked like the aux batt was in place.

But yesterday I had one, and the whole vehicle shut down. Engine died, lights out, etc. Right away I realized I had an ESS event, but for some reason it didn't act like the aux batt was in place.

Knowing the relay is NC, whats happening is that the relay was stuck (in the NC position) and that would be the same behavior as pulling F42. Also after that last ess event, now I get the ESS not ready warning. probably now during the aux batt check during start up, it can see there's no voltage on the aux batt cables.

My guess is the relay had been stuck for a while, and finally decided to bust loose and start working.

So now I'll strap the aux plus cable to the main, and pull the F42 fuse.

 

[THAW]

So now I'll strap the aux plus cable to the main, and pull the F42 fuse.

Technically, only one of those two changes is necessary to fix your dash light (though doing both doesn't hurt).

 

[Max Headroom]

Technically, only one of those two changes is necessary to fix your dash light (though doing both doesn't hurt).

Hey, thanks for pointing that out. I hadn't thought that all the way thru, but you are correct, either will do the same thing.

 

[Dmb2002man]

I just want to say I have a 2020 Sahara with 25k miles and replaces aux battery twice now. I replaced my main battery with h7 850cc when I did the aux. I finally removed fuse f42 and disconnected negative aux battery. No issues at all. I charge aux once a month. I only charge since it's brand new but should of never replaced it the second time. That aux battery is a joke.

 

[Magnus Taterhawk]

I am a novice no doubt I am a 58yo novice, but i love this jeep. my friend has the gray Rubi he lost his job had to put it up for sale on local lot and I am left adrift to handle these little add ons by myself. Oh sure my nephew comes to stay with us he 14 and has no love for the Jeep such as I. I too have watched my ESS bat suck down my main AGM H6 with 750 crank amps. I disconnected the neg cable and pulled fuse. I have a Tazer. I kept getting the "A!" and "service air bag", and other happy horsesh#t. I gave up. Then I watched some youtube jockys remove ESS battery from down under and black tape the neg and then spend a loooong time trying to thread the Pos up thru the tray and reattach to the main battery. I thought hell I can bolt a large gauge wire to Pos run it up to the main battery in like no time flat.
I hope this works. We will see. By the way someone needs to nut thump the engineer that came up with the ESS crap, HARD!!!!

 

[THAW]

By the way someone needs to nut thump the engineer that came up with the ESS crap, HARD!!!!

 

[Dmb2002man]

I am a novice no doubt I am a 58yo novice, but i love this jeep. my friend has the gray Rubi he lost his job had to put it up for sale on local lot and I am left adrift to handle these little add ons by myself. Oh sure my nephew comes to stay with us he 14 and has no love for the Jeep such as I. I too have watched my ESS bat suck down my main AGM H6 with 750 crank amps. I disconnected the neg cable and pulled fuse. I have a Tazer. I kept getting the "A!" and "service air bag", and other happy horsesh#t. I gave up. Then I watched some youtube jockys remove ESS battery from down under and black tape the neg and then spend a loooong time trying to thread the Pos up thru the tray and reattach to the main battery. I thought hell I can bolt a large gauge wire to Pos run it up to the main battery in like no time flat.
I hope this works. We will see. By the way someone needs to nut thump the engineer that came up with the ESS crap, HARD!!!!

Upgrade to h7 and everything would go away 850cc

 

[Amaruq]

I think my aux battery has drained my main and my jeep won’t start.
a few years ago, I replaced my main with a bigger/better one suggested by this forum. Never got around to disconnecting the aux. I suspect it’s happened again. Is there an easy, quick fix? Or do I need to have the aux removed/disconnected properly and replace my main battery again? I can just pull a fuse and start her up, can I?

2020 3.6L Manual. Have had the ESS unavailable light and dash message in the menu since forever.

 

[YGBSM392]

Damn, I have to pay fifty bucks for that downtown!

Anyone have her number? Asking for a friend...

 

[charlie00tj]

My 2019 JLU 2.0 started giving the Aux ports not working because charging battery message so I decided to do the aux battery delete and disable ess. I disconnected the negative battery cable from the aux battery but I do not have a fuse in 42. I'm the original owner of the Jeep and I did not remove it. The Jeep starts fine and I still get the battery charging message.

 

[THAW]

My 2019 JLU 2.0 started giving the Aux ports not working because charging battery message so I decided to do the aux battery delete and disable ess. I disconnected the negative battery cable from the aux battery but I do not have a fuse in 42. I'm the original owner of the Jeep and I did not remove it. The Jeep starts fine and I still get the battery charging message.

A 2019 2.0L has eTorque, so doesn't have an AUX (ESS) battery, AUX (ESS) ground cable, or F42 fuse from factory. So, the question is what ground cable did you disconnect?

The AUX Switches unavailable and battery charging messages mean you need to replace your CR[an]K/main battery.

 

[yarmo]

This might be a silly question, but has anyone ever had a dealership give them an issue with warranty coverage due to deleting the aux battery/disabling the ESS system?

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