AUX battery delete/bypass - Which method is proper?

[Zjamison]

Every since this post https://www.jlwranglerforums.com/forum/threads/ess-battery-cable-change.86624/ I've opted to use guidance wording that has the Aux battery deleting owner visualize the distal end of the cable that they are (not) removing from the main battery's negative post (i.e. the body ground cable) as this guidance is generic enough, I hope, to withstand factory cable changes across model years.

Thanks again! that's a great thread and is a lot of help.

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[AndySpill]

Is there harm in just connecting auxiliary POS and neg to the main without removing fuse 42?

I can't help but infer that your question asks if it is harmful to keep dual AGM battery JLs configured as they were from the factory. Maybe I am missing something.

The answer is that it certainly is not harmful. What it may be though is not beneficial, perhaps its costs not worth its benefits.

Stellantis choice to use two batteries for its ESS system, a bit of a departure in the industry, may have introduced a bit of a monkey wrench when in outfitted two AGM batteries of different sizes were connected in parallel 99.9% of the time. The smaller battery can cannibalize the larger one over time, and the fuel savings, while measurable, is relatively low, particularly when properly counterbalanced against the green footprint of the technology of the system itself, the ever growing battery graveyard, and wear and tear on vehicle components from the more frequent engine starts and stops.

Particularly for short time, infrequent usage, cold climate owners, tricking charging may be all but necessity if both batteries are kept as per factory--which by the way, just so conflict of interest is revealed here, something I continue to do.

A better mousetrap might have involved identical batteries that switch off roles as main and Aux. But that would have cost us more at purchase time, and Stellantis goal was passing the EPA's (IMHO) poorly written guidelines for dealers to enjoy the mileage ratings of employing an ESS system and passing CAFE standards, not about what owners might face in problems down the road from a system designed to merely pass a one time test.

I blame the EPA. Devising policy that gets a vehicle's ESS system to simply engage pre-purchase in a model for manufacturers to devise the most cost effective way to pass that test, not save gasoline as the policy was originally designed for. In fairness, I'm sure the EPA had plenty of lobbyists knocking on their door to make their guidelines as simple to pass as possible.

 

[Grayhound]

I can't help but infer that your question asks if it is harmful to keep dual AGM battery JLs configured as they were from the factory. Maybe I am missing something.

The answer is that it certainly is not harmful. What it may be though is not beneficial, perhaps its costs not worth its benefits.

Stellantis choice to use two batteries for its ESS system, a bit of a departure in the industry, may have introduced a bit of a monkey wrench when in outfitted two AGM batteries of different sizes were connected in parallel 99.9% of the time. The smaller battery can cannibalize the larger one over time, and the fuel savings, while measurable, is relatively low, particularly when properly counterbalanced against the green footprint of the technology of the system itself, the ever growing battery graveyard, and wear and tear on vehicle components from the more frequent engine starts and stops.

Particularly for short time, infrequent usage, cold climate owners, tricking charging may be all but necessity if both batteries are kept as per factory--which by the way, just so conflict of interest is revealed here, something I continue to do.

A better mousetrap might have involved identical batteries that switch off roles as main and Aux. But that would have cost us more at purchase time, and Stellantis goal was passing the EPA's (IMHO) poorly written guidelines for dealers to enjoy the mileage ratings of employing an ESS system and passing CAFE standards, not about what owners might face in problems down the road from a system designed to merely pass a one time test.

I blame the EPA. Devising policy that gets a vehicle's ESS system to simply engage pre-purchase in a model for manufacturers to devise the most cost effective way to pass that test, not save gasoline as the policy was originally designed for. In fairness, I'm sure the EPA had plenty of lobbyists knocking on their door to make their guidelines as simple to pass as possible.

My question is can I remove the auxiliary battery and just install the aux battery cables on the main battery without pulling fuses and get it to run without check engine lights and operate normally?

 

[THAW]

My question is can I remove the auxiliary battery and just install the aux battery cables on the main battery without pulling fuses and get it to run without check engine lights and operate normally?

Yes, except you'll be limited to 6 ESS cycles per trip (i.e. ignition button vehicle start).

Note that attaching the ESS/aux battery cable negative terminal connector to the main battery negative terminal is unnecessary for your method of maintaining (essentially) normal vehicle functionality after removing the ESS/aux battery - but is useful for keeping the cable secured.

 

[AndySpill]

To Foster's @THAW's point, not that I recommend that you run ESS events with one battery on a "from the factory" dual AGM battery JL, but the fact is that each time you do engage ESS with an single cold engine crank the vehicle will note the the Aux battery--or should I say what it thinks is the Aux battery's, which is really the main battery's voltage, and how it is identical to the main battery's voltage (no surprise as that same battery is being tested in isolation.)

The vehicle assumes this could only be the case, given untouched factory wiring, if somehow the batteries aren't being separated in ESS events, and if it happens 6 times within a cold crank, as Foster accurately reports, the vehicle will shut ESS off for you for the remainder of that cold crank.

This is why the Genesis Offroad kit is limited to 6 ESS events per cold crank, which in this poster's opinion is hardly a reason to not get this otherwise wonderful kit if you happen to run a fair share of appliances with the engine off.

The kit is not though an alternative for running factory ESS events; I mean it could but it's not the kit's indication and its cost is better spent elsewhere if on the continuum of Jeep owner one gravitates more to paved than offroad experiences--if you catch my drift.

 

[YBABRAT]

If disconnecting aux battery always remove F42. If leaving it in place it will throw a code and effect readiness.

 

[kris77]

I was getting ready to remove 42 and the negative wire but I only have 1 wire connected. Is there another place the factory would have connected the ground?

 

[Buddy Lee]

I was getting ready to remove 42 and the negative wire but I only have 1 wire connected. Is there another place the factory would have connected the ground?

If you only have one wire you have the Etorque module and don’t have an auxiliary battery. Instead you have a 48v battery under the drivers side passenger seat.

 

[kris77]

No, I'm pretty sure have the aux battery. I can see it from the inner fender. I'm getting the "aux switches not working, battery is charging" message. Was gonna replace the main and delete the aux. Do you think that aux battery box is empty then?

EDIT: I just started doing research on etorque and I'll have to look when the wife gets home. It looks like I might have that model. I had no clue. I probably should have known that from the beginning. Guess I just overlooked it. I wonder if that extra 8yr 80k mile warranty covers the main battery?

 

[Max Headroom]

If disconnecting aux battery always remove F42. If leaving it in place it will throw a code and effect readiness.

New to the forums, and new to owning a Jeep with the ESS.
First off, I HATE these start stop vehicles!
Secondly I've been lurking here for about a month trying to educate myself about the dual battery ESS, the HPFP issues, and such.

My ride is a 21 JLURD. About a week into my ownership my remote start would fail first thing in the morning. It's been very cold here, and it looks to be the original battery. The RS would work after the vehicle had been started normally and driven. Or would work if I ran the battery tender.
So my assumption was the system was detecting a weak aux batt on my initial morning start.

OK, that said I went out and bought new batteries. After having read numerous threads (including the 50 page one) about the second battery being a problem, and cannibalizing the main battery once the aux starts to age (which seems to happen a lot quicker than the main) I decided to try not using the aux on my battery swap.

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.
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.
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?
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.

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

 

[AndySpill]

My question is can I remove the auxiliary battery and just install the aux battery cables on the main battery without pulling fuses and get it to run without check engine lights and operate normally?

Yes, as my 3rd sentence says. Sorry if I got on my soapbox there.

 

[THAW]

New to the forums, and new to owning a Jeep with the ESS.
First off, I HATE these start stop vehicles!
Secondly I've been lurking here for about a month trying to educate myself about the dual battery ESS, the HPFP issues, and such.

My ride is a 21 JLURD. About a week into my ownership my remote start would fail first thing in the morning. It's been very cold here, and it looks to be the original battery. The RS would work after the vehicle had been started normally and driven. Or would work if I ran the battery tender.
So my assumption was the system was detecting a weak aux batt on my initial morning start.

OK, that said I went out and bought new batteries. After having read numerous threads (including the 50 page one) about the second battery being a problem, and cannibalizing the main battery once the aux starts to age (which seems to happen a lot quicker than the main) I decided to try not using the aux on my battery swap.

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.
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.
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?
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.

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

Used vehicle? Have you confirmed the AUX (ESS) battery ground cable is attached to the CR[an]K (aka main) battery negative terminal and fuse F42 is in place (i.e. that the previous owner didn't already bypass the small battery)?

 

[Max Headroom]

Used vehicle? Have you confirmed the AUX (ESS) battery ground cable is attached to the CR[an]K (aka main) battery negative terminal and fuse F42 is in place (i.e. that the previous owner didn't already bypass the small battery)?

Yes, the battery set up was in the stock config, and the F42 fuse in place

 

[THAW]

Yes, the battery set up was in the stock config, and the F42 fuse in place

No jumper on the N1 post?

The scenario you're describing doesn't make sense to me, since in the factory configuration the PCR opening without an AUX (ESS) battery in place would kill system electronics. You should at least get a dash warning light.

 

[Max Headroom]

No jumper on the N1 post?

The scenario you're describing doesn't make sense to me, since in the factory configuration the PCR opening without an AUX (ESS) battery in place would kill system electronics.

No jumper on N1, or N2 or N3.
Right, according to all I have read, you would be correct. It doesn't make sense to me either, based on all I have read about this.
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.
So when I noticed that I opened up the fuse box and looked for a jumper, and there was none.
FWIW, the main and aux were both Mopar factory batteries, and the engine compartment, including the wire looms look virgin. In fact the engine compartment could have passed for a new vehicle when I first look at the jeep. I don't feel like the prev owner had done anything here.
I read the thread about the late 21 wiring change, but didn't quite understand the implications of the changes, but I feel like this one is potentially one of those vehicles. It's confusing, for sure.
Been almost a week running like this, and all seems well. No codes, no messages, normal voltages, remote start works. Weird, but happy it's just acting like a normal car.
Been single digit temps here, but when it warms up a little I want to pull the F42 fuse and see if it behaves differently. Just as a test.

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