Aux battery bypass

[azwjowner]

I installed an ESS defeat harness the day the new Jeep was driven home from the dealer.

My OEM H6 AGM lasted four years, almost to the day. It spun the starter just fine the evening prior, and then was dead as a doornail the following morning. I replaced it with an Interstate H7 AGM, isolating the ESS battery at the same time and via the accepted method. Done.

Not once during my ownership have I had a battery charger of any type connected to the batter(ies) in my JLU.

I’m at 37 months on stock batteries, also disabled ESS on day one with a smart stop start device. I’ll preemptively replace the main, upgrade to an H7, and remove the aux this fall.

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[Rhinebeck01]

The aux battery first started being bypassed in 2018, the jumperless bypass was the 2022 improvement. https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/post-423590

@Rhinebeck01 was the bleeding edge and has been running it ever since.

Time flies.... Yes, tail end of 2018 I did the fused jumpered bypass on my JL... and have driven over 105,000 with one in place..

Thanks once again, to @Jebiruph (Jerry) for assembling and sending to me (which I installed) what was undoubtedly theeeee 1st fused, jumpered bypass ever created for a Wrangler JL.

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[Mguy]

.Time flies.... Yes, tail end of 2018 I did the fused jumpered bypass on my JL... and have driven over 105,000 with one in place..

Now that's an accomplishment!

Maybe others from your "generation" of early adapters will post. I hope to be proved wrong about having to wait for a report of single battery longevity without external charging.

I do think that it was @Jebiruph's aux negative/F42 innovation that started widespread understanding and single battery use. I thank you both for the very good work in making this solution avalable to us all.

 

[AndySpill]

If someone is making the claim that dual AGM battery JLs, with ESS turned off, are experiencing longer (not just as long) main battery life than those in which ESS is also turned off, but the Aux battery is bypassed, then I suppose that might be a justification for keeping the Aux battery connected even if it never runs ESS events, at least until it's time to replace the batteries, where the added expense of also purchasing the Aux battery can be considered versus bypassing it.

But if this claim can't be substantiated I am of the mindset, in this case at least, that the adage “Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away” might best apply, and that disconnecting the Aux battery in such cases guarantees that its demise, from whatever cause (even if that's far more from the process of prior running of ESS events that are no longer happening here, than say as a result of a crappy Aux battery's failure), if you don't need it as a result of turning ESS off, don't keep the Aux battery connected.

Perhaps there exceptions for some owners running appliances with the engine off that makes the additional amp hours of having this Aux battery connected outweigh its risk of cannibalizing the main battery.

@THAW I cannot help but believe, and you can correct this if I've got it wrong, that you almost would sooner advocate, paradoxically enough, keeping the factory connections on dual AGM battery JLs where owners have turned ESS off, and elimination of the Aux battery (or at least little harm in its elimination) for such owners that do run ESS events.

 

[THAW]

@THAW I cannot help but believe, and you can correct this if I've got it wrong, that you almost would sooner advocate, paradoxically enough, keeping the factory connections on dual AGM battery JLs where owners have turned ESS off, and elimination of the Aux battery (or at least little harm in its elimination) for such owners that do run ESS events.

You're on to something, but in the Jumperless AUX Bypass paradigm there's no paradox; the thought one still exists is a product of forum orthodoxy around false mutual exclusivities contradicted by widely reported forum-user experience (namely, if the AUX battery is electrically removed ESS must be disabled, and if ESS is used the AUX battery must be electrically retained).

For a JL owner who consistently/permanently disables ESS, I don't "advocate" exclusively for retaining the AUX (ESS) battery, since removing it also works and both configurations have battery-life preservation effects (overall cycling minimization, plus significant DoD minimization for a connected AUX battery persistently part of a larger bank).

TLDR: a tiny battery used hard during ESS events fails fast, so to conveniently improve (non-eTorque, non-4xe, excl. 392) JL 12V battery life do at least one:

• disable ESS
• electrically remove the AUX (ESS) battery

...than say as a result of a crappy Aux battery's failure

If the AUX (ESS) battery is likely to be intrinsically malignant, one should definitely not leave it connected for the purpose of the same ESS operation that inherently accelerates its wear - especially since forum gospel dictates batteries be replaced in pairs.

 

[THAW]

@THAW, first, regarding your statements on battery capacity and internal resistance, the problem is they are just that, statements. Rather than ask a question about batteries, you posted useless tautologies. Just as Lucy doesn't need to know much about football when playing with Charlie Brown, you don't need to know much about batteries to cite a technical term or two. But I'm not going to be Charlie Brown in your trolling game.

As for substantiating my assertion that among non-ESS users dual battery stock setups will likely not do as well as those with the aux negative/F42 disconnect, readers still interested and unsure should look again at my first post in this thread. JLs with a single battery don't suffer from the two deficiencies there identified. Some may note the small capacity increase from the aux battery. While not mentioned, I think it common knowledge among regular users of 12 volt AGM systems that good charging maintenance--which single battery setups promote and make easy--can overcome other battery characteristics, including small capacity differences. So I'm not sure, but believe it likely, that single battery JL setups will last longer.

Finally, for anecdotal evidence regarding JL single battery use, we'll have to wait. The aux negative/F42 disconnect mod wasn't even invented until June, 2022, less than three years ago.

Got it, so you condescendingly doubted verifiable claims, and "informed" with an unsubstantiated guess based on exaggerated, myopic interpretation of generic battery "science" that caused you to underestimate empirical battery bank life, but still essentially repeated recommendations provided in the posts you criticized. Sounds like trolling to me.

 

[AndySpill]

Is it supposition or fact that dual AGM battery JLs, which have their ESS system turned off, on the whole fair better than those setups where ESS is also turned off, but the Aux battery is bypassed? Or do they fair no better or worse on the whole?

For me that decision, regardless of its outcome, weighs the additional amp hours of these two batteries connected in parallel, versus the potential for either battery to reach the end of its useful like faster than the other, and bring down the "good" battery with it.

I do appreciate the paradox here that the seeming #1 reason for an Aux battery to age faster and cannibalize the main battery is the very running of ESS events solely on this battery, something that a fused jumper or Fuse 42 or turning ESS off pull would prevent.

If the vehicle fairs no better with ESS off and the two batteries connected, I'd say that bypassing the Aux battery is the path of least resistance (no pun intended) as a disconnected Aux battery that craps out, for whatever reason, even if not because it's been running ESS events alone, is a battery than can't negatively effect the main battery.

If the vehicle fairs better with ESS off and the two batteries connected, I'd be interested in knowing just how much better to see if these pros outweigh the cons of these dissimilar sized batteries being connected in parallel. And I would especially want to see significant benefit, when it comes time to change batteries, that keeping the factory configuration, at greater two battery purchase expense, outweighs just buying a new main battery and bypassing the Aux.

I have no horse in this race. I run factory dual AGM battery setup, ESS events, and trickle charge.

 

[Heimkehr]

Is it supposition or fact that dual AGM battery JLs, which have their ESS system turned off, on the whole fair better than those setups where ESS is also turned off, but the Aux battery is bypassed? Or do they fair no better or worse on the whole?

I'm hoping to have an answer to that very question, but only after sufficient time passes.

The ESS function in my then-new Jeep was disabled with the related harness on the same day that I drove the vehicle home from the dealer. The OEM H6 AGM main battery lasted four years, almost to the day, and for that sum of time it didn't have to provide power for the ESS events that weren't occurring anyway. Note that the separate ESS battery wasn't ever isolated when the H6 was still in situ, either.

I isolated the ESS battery, via the accepted two-step method, after installing a new Interstate H7 AGM battery last October. The aforementioned harness remains in place and working, so to speak, so we'll see how long the H7, which is now well and truly a solo act, lasts.

 

[AndySpill]

I'm hoping to have an answer to that very question, but only after sufficient time passes.

The ESS function in my then-new Jeep was disabled with the related harness on the same day that I drove the vehicle home from the dealer. The OEM H6 AGM main battery lasted four years, almost to the day, and for that sum of time it didn't have to provide power for the ESS events that weren't occurring anyway. Note that the separate ESS battery wasn't ever isolated when the H6 was still in situ, either.

I isolated the ESS battery, via the accepted two-step method, after installing a new Interstate H7 AGM battery last October. The aforementioned harness remains in place and working, so to speak, so we'll see how long the H7, which is now well and truly a solo act, lasts.

So when it came time to replace batteries James you, it seems, attempted to test the theory (on which the jury is still out for you of course) that the purchase of an additional new Aux battery, in addition to your new H7 main, might not yield you benefits worth the additional Aux battery cost, and bypassing the Aux was an avenue at least worth trying.

I'd be surprised to find many factory dual AGM JL owners, who turn off ESS, buying both batteries when the time comes to replace the main battery.

 

[Mguy]

Perhaps I'll still be here at year's end and able to provide a report on a Mopar H7 then at five years working alone that has thus far never seen a charger or needed a boost. In the mean time, the result of a recent load test can be found at post #286 in this thread.

 

[JINO]

Isolating the ESS battery is dead simple: Remove and tape off the related Negative cable, and remove Fuse F42 from the PDC (aka fuse box.)

Restoring ESS functionality for dealer visits during the warranty period is the inverse of the two-step disabling process. Done.

I did this with my 2021 ecodiesel and it would not start. Plugged fuse back in and it started (without aux terminal). Taped it up and left it like that. Not sure why or how, but works for me.

 

[Mguy]

I did this with my 2021 ecodiesel and it would not start. Plugged fuse back in and it started (without aux terminal). Taped it up and left it like that. Not sure why or how, but works for me.

Seems like the PCR (Power Control Relay) wasn't, or isn't, working properly. The PCR is a normally closed switch, meaning power normally runs through it's controlled circuit. The aux negative/F42 disconnect makes use of the controlled circuit for providing power to the N1 loads, which are essential for vehicle operation. So, if the PCR is stuck open there is no power to N1 and the Jeep can't work.

F42 fuses the control circuit for the PCR. Could be that when you reinserted F42 the PCR was reactivated and returned the controlled circuit to it's normally closed position.

Things may continue to work fine for you. But if there is a PCR issue, two good choices for reliability include, 1) replace the PCR, or 2) install a heavy jumper to N1 from one of the several positive sources (N2, 3, or 4, or the main battery bus).

Given your initial problem, the second choice would be good insurance.

Best of luck.

 

[AndySpill]

Seems like the PCR (Power Control Relay) wasn't, or isn't, working properly. The PCR is a normally closed switch, meaning power normally runs through it's controlled circuit. The aux negative/F42 disconnect makes use of the controlled circuit for providing power to the N1 loads, which are essential for vehicle operation. So, if the PCR is stuck open there is no power to N1 and the Jeep can't work.

F42 fuses the control circuit for the PCR. Could be that when you reinserted F42 the PCR was reactivated and returned the controlled circuit to it's normally closed position.

Things may continue to work fine for you. But if there is a PCR issue, two good choices for reliability include, 1) replace the PCR, or 2) install a heavy jumper to N1 from one of the several positive sources (N2, 3, or 4, or the main battery bus).

Given your initial problem, the second choice would be good insurance.

Best of luck.

To Mike's last option above:

https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

 

[Mguy]

To Mike's last option above:

https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

Thanks for following my post but I believe the thread you cited is not very useful for JL owners who, for whatever reasons, are interested in a jumper solution for some aspect of the stock dual battery setup. Much of the information on that subject is just dated and not very helpful any more.

 

[AndySpill]

Thanks for following my post but I believe the thread you cited is not very useful for JL owners who, for whatever reasons, are interested in a jumper solution for some aspect of the stock dual battery setup. Much of the information on that subject is just dated and not very helpful any more.

Ok, but I disagree.

The post I linked shows pictures of the very "heavy jumper to N1 from one of the several positive sources (N2, 3, or 4, or the main battery bus)" that you cited.

Like yanking Fuse 42 this solution, as I suspect you know, and the original method before Jerry @Jebiruph identified the (PCR) Power Control Relay Fuse 42 connection, prevents the Aux battery connections from being isolated.

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