Auxiliary Battery Elimination

[mbrose1994]

sorry I do not get it. do you have some pictures? which 2 +? disconnect?

What is CRK? apologies for my short-hand: CRK == Crank or Primary battery
What is N2 vs N1? The high amp fuse array on right side of PDC box.

That bank has N1 -> N7. Factory has 2 positive (POS) cable ends connected to this array.
The are connected at N1 and N3 locations.
I took both those off.

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[AndySpill]

Update post.
Have achieved simple, total, absolute electrical separation from Jeep's Rube Goldburg AUX batt design.

Just disconnect and tape off (electrical tape) all (1 NEG, 2 POS) AUX batt cable ends.
Leave CRK batt POS cable end on N2.
Jump N2 to N1.
Done.

No remove/replace the right front fender.
No remove/reinstall PCM box.

I'm going to try to decipher this for you @Cartman .

Michael seems to report a a classic Aux battery bypass, minus the Fuse 42 pull.

This is fine to do if you jumper N1 to N2 (these are parts of the high amp fuse array on the driver's side portion of the Power Distribution Center (PDC), closest to the front of the vehicle : the vehicle's intelligent fuse box. In fact the original technique to effect this bypass, before the Fuse 42 trick was discovered and reported by @Jebiruph, was to stick a fused jumper between N1 and N2

Fuse 42 powers the Power Control Relay (PCR): a normally closed relay that only when energized separates the AGM batteries in dual AGM battery equipped JL: an event that open happens for an instant pre cold crank and during ESS events.

Keeping Fuse 42 in place, while it allows the PCR to separate the batteries, becomes moot in terms of the electrical schematic of the vehicle because the aforementioned fused jumper has hard wired the batteries together such that all calls for power go to all batteries that are connected, if which only one is in this case: the main battery.

In terms of Michael's description that the Aux battery need not be removed, either from the side thru the fender, or the top by removing the PDC: nether was required under the Fuse 42 pull method either. That Aux battery can sit where the factory put it, unattached.

@Cartman: if this detail isn't already known to you, IMHO you had no business putting down the Aux battery bypass of my other thread, which let me assure you is nothing personal. I run both batteries factory: it was just a survey question.

 

[Cartman]

thanks, i understand now.
In the future I plan to replace AUX and then try to reconnect it.
funny things is, that after disconnecting AUX negative and removing fuse 42 my Start/stop starts working. It never works and I was confident with this. I tought that if I will disconnect AUX the Start/stop will still not be working.

 

[AndySpill]

thanks, i understand now.
In the future I plan to replace AUX and then try to reconnect it.
funny things is, that after disconnecting AUX negative and removing fuse 42 my Start/stop starts working. It never works and I was confident with this. I tought that if I will disconnect AUX the Start/stop will still not be working.

@Cartman I feel sorry for you. You don't want to read, and without doing so you will not learn.

One more time. I'll try to keep this short for you.

At cold crank the dual AGM battery version of the JL, out of the factory, energizes the Power Control Relay, a normally closed relay powered by Fuse 42 to separate the batteries and test the Aux battery alone.

Pulling Fuse 42 means the batteries can't be separated, all unknown the vehicle, so any calls for battery power go to both batteries....

except you disconnected your Aux battery, so all calls for battery power to either or both batteires not go only to the main battery.

So your vehicle tests the main battery at pre crank thinking it's tested the Aux and effectively says to itself, "wow this Aux battery (which really is the main battery) has really strong power," thereafter permitting ESS events to happen.

The short version: you've tricked your vehicle into thinking the main battery is the Aux battery.

I would turn off the ESS system now at the button or by tech to do it automatically for you. While most vehicles run ESS systems on one battery, I am not comfortable advising this in a Wrangler, where people can run power hungry aftermarket appliances, at long traffic lights, on cold nights, with aging main batteries, on busy roads, where that main battery is possibly depleted of power to crank before the ESS events terminates early.

This is not a concern under the factory setup because the main battery is spared during ESS events and appliances are run off the ESS battery.

 

[Nash_Dj]

Funny things is, that after disconnecting AUX negative and removing fuse 42 my Start/stop starts working. It never works and I was confident with this. I thought that if I will disconnect AUX the Start/stop will still not be working.

ANDREW, I am also in a deep investigation what is the best way to do it and what are the results - pros and cons, so I can do my new Jeep safely and effectively. However, and to be fair to @AndySpill who put tremendous energy and his time in explaining it to dummies (like me), reading all those posts I think I now have a good understanding of the Jeep's design, the proposed hack to improve it, as well as common misunderstanding theme in almost every post...

What I found as a common MISUNDERSTANDING by people getting in to this topic, is the fact that the hack ONLY eliminates the AUX battery from the electrical circuit (and as Andy explained it already, it redirects all power needs just to the main battery), but has NOTHING to do with the Stop/Start (ESS) feature. Whether you do the hack or not, the ESS events still happen as designed, but if you do the hack the Stop/Start power draw is on the MAIN (CRanK)battery which was not designed for that. Hence, the need to either meticulously disable the ESS feature by pushing the button on the center console as soon as you turn on your Jeep, or simply, more efficiently and far more safer, use one of those electronic devices, like Autostop eliminator or TazerMini, to permanently disable the feature. Again, the hack is only to "eliminate" the AUX battery to save the main battery, not to eliminate the Stop/Start...
Hope this helps.

 

[Cartman]

Partialy understood.
I partially understand.
1. I disconnected the negative pole from the AUX battery - that removed it from the system
it just means that the large battery must replace the small one.

2. I removed fuse 42 which, in my opinion, disabled the relay that is supposed to switch which battery is charging when and if this relay is malfunctioning, only the large battery is always charging. Am I wrong?

If I understand correctly, then:
- The AUX battery is not AGM - because it is not used to start the engine and has 14-19Ah and is used when the engine is turned off at a traffic light, the alternator does not charge the battery but the small battery powers the air conditioning, radio, lights and so on at that moment.,...

- The large battery is AGM and has about 70Ah and is always used mainly to start the engine as initially and with every Start/stop. It is also primarily charged so that it is always ready to start the engine.

The funny thing is that the system is supposed to check itself whether it is appropriate to use Start/stop.
Until now, when my aux battery did not work, it always evaluated that the system was not ok and Start stop did not turn on. Now, after disconnecting the AUX, during the check, it seems that it did not detect that the AUX battery was not in the system and checks the belts and hood and voltage and other things and evaluates that everything is OK and turns on Start/stop.
Simply put, the check overlooks the disconnected AUX battery.

 

[Red Rubi 22]

This:

 

[entropy]

Everyone please keep in mind starting 2024 the negative wires were swapped. So disconnecting the negative cable closest to the passenger side will NOT isolate the aux battery. By doing this and trying to either charge the batteries or turn on your Jeep you could damage electrical components. So be careful.

 

[mbrose1994]

Partialy understood. <...snip...>
Simply put, the check overlooks the disconnected AUX battery.

Yes, which is expected by Jeep design.
The check only "sees" and measures the CRK batt.
Which, so long as it has sufficient charge, the ESS system is happy and works as designed.

The cavet is the CRK battery is not well suited for the ESS drain when the engine is Auto-Stopped.
Which is why you see the advice to disable the ESS system with either the factory button or adding a device to automatically disable the ESS every time you start the Jeep.

I am satisfied with the factory button.

But, I am assuming the risk that
if I forget to manually use the factory button,
and I have a weak/dying CRK battery,
and significant drain on the CRK batt while stopped,
then my Jeep could fail to Auto-Start.

And I then I get stuck on the road with a dead Jeep.
It is a "what are you willing to risk decision".

 

[Red Rubi 22]

Everyone please keep in mind starting 2024 the negative wires were swapped. So disconnecting the negative cable closest to the passenger side will NOT isolate the aux battery. By doing this and trying to either charge the batteries or turn on your Jeep you could damage electrical components. So be careful.

As far as I know, the aux battery negative cable connected to the main battery is always the smaller diameter cable despite what the end connection point looks like. So make sure to disconnect the smaller cable.

 

[AndySpill]

Partialy understood.
I partially understand.
1. I disconnected the negative pole from the AUX battery - that removed it from the system
it just means that the large battery must replace the small one.

More precisely stated, by disconnecting the negative cable from the Aux battery, and in so doing preventing it from completing an electrical circuit, you have taken it out of the vehicle's electrical schematic, to never be charged or charge things thereafter. This step alone will not, at least without producing errors in the dash, allow the large battery to replace the small one, in fact in early 2018 models, this disconnection alone would strand the vehicle (unless you had a dealer apply TSB 18-902-19.

In colloboration with this cable pull, pulling Fuse 42 prevents the batteries from being separated such that all calls for the Aux battery to provide power, be it alone for an instant at start up, alone during ESS events, or in tandem with the main battery at all other times, now gets redirected to all connected batteries, if which you have one: your main.

These 2 steps can and will, as you say, have the large battery replace the small one.

If you preferred, you could have jumped N1 to N2 instead of (or in addition) to pulling Fuse 42. Both actions, alone or in tandem, prevent the batteries from be separated.

2. I removed fuse 42 which, in my opinion, disabled the relay that is supposed to switch which battery is charging when and if this relay is malfunctioning, only the large battery is always charging. Am I wrong?

Removing Fuse 42 alone prevents the batteries from being separated. Both batteries normally participate in being charged or powering appliances, but for ESS events in the factory configuration where the Aux battery powers appliances.

It is this fuse pull along with disconnecting the Aux battery that allows only the main battery to accept or delivery charge.

The relay that separates the two batteries in the dual AGM battery JL, the Power Control Relay (PCR) rarely is energized, only receiving power in the factory configuration during ESS events and an instant at cold crank to allow the Aux battery to be tested independent of the main battery. This relay is considered, in relay speak, a normally closed relay, the "closed" referring to a closed circuit in which electrons can travel when power is NOT provided to the relay.

A normally open relay might, for example, power your vehicle turn lights as when power is not applied to the relay these lights remain off.

While I imagine that its possible that this relay could get stuck in its open position, even when electrical current is withdrawn from it, I'd consider it far more likely, because it is a normally closed relay, that if it fails, that it would fail in the closed position.

If I understand correctly, then:
- The AUX battery is not AGM - because it is not used to start the engine and has 14-19Ah and is used when the engine is turned off at a traffic light, the alternator does not charge the battery but the small battery powers the air conditioning, radio, lights and so on at that moment.,...

- The large battery is AGM and has about 70Ah and is always used mainly to start the engine as initially and with every Start/stop. It is also primarily charged so that it is always ready to start the engine.

It is generally true as you mention that during ESS events, that under the factory configuration, the ESS battery solely energizes vehicle appliances. Some things like power steering though have been tested to run off the main battery. Perhaps this is why that one of the many conditions that will prevent ESS from engaging is a steering wheel that is turned too far in one direction.

AGM stands for an absorbent glass mat. Both batteries in the "dual AGM battery JL" (by its very name) are of this type. It is a variant of a sealed lead acid (SLA) battery that excels at more quickly delivering and recovering charge than its predecessor.

Batteries connected in parallel as these two are from the factory almost invariably need to be of the same chemistry. Ideally they should also be of the same size but aren't here. Parallel means that their positive posts are connected and their negative posts are connected, but these two cables are insulated from one another. Parallel connections increase amps and equal out voltage between the batteries. It provides more power but introduces risk that a bad battery in the connection can cannibalize a good one: particularly when the batteries alone are of different sizes.

Out of the factory both AGM batteries are used to cold crank the engine (crank at start up.) At the end of an ESS event, I believe, but am not sure, that given the factory connections, only the main battery cranks the engine. From the factory I am not of the belief that one battery has charge precedence over the other when the engine is on. The are connected as unit.

The funny thing is that the system is supposed to check itself whether it is appropriate to use Start/stop.
Until now, when my aux battery did not work, it always evaluated that the system was not ok and Start stop did not turn on. Now, after disconnecting the AUX, during the check, it seems that it did not detect that the AUX battery was not in the system and checks the belts and hood and voltage and other things and evaluates that everything is OK and turns on Start/stop.
Simply put, the check overlooks the disconnected AUX battery.

..and this is why @Cartman you need to read. One more time: Translate this into Slovak if you need to. I say that void of any editorial comment. Neither the people of Slovakia nor the U.S. are better or worse than the people of any other country.

* Before you disconnected the Aux battery and Fuse 42 the pre engine crank test isolated your Aux battery by turning on the PCR, felt that the Aux battery lacked sufficient power, turned off ESS, reconnected the two batteries and both cranked your engine.

* After you disconnected the Aux battery and Fuse 42 the pre engine crank was unable to separate the batteries. Unknown to the vehicle the pre-crank test of the ESS battery went against all available batteries, if which you only have one: your main. The vehicle, tested your main battery thinking it was your Aux, was impressed with the power it showed, and allowed the ESS system to turn on should the situation arise. As @Nash_Dj mentions, disconnecting your Aux/ESS battery and turning ESS off are entirely two separate things. Ironically enough, here was situation where disconnecting your Aux/ESS battery actually helped turn ESS back on.

Your vehicle had no idea the Aux battery was disconnected. There was no detection. It thinks it was still there as there is no check by the vehicle that Fuse 42 was pulled or the Aux battery was disconnected with only this caveat: if you had just disconnected the Aux battery but not pulled Fuse 42 (or jumpered N1 to N2,) your post 2018 Wrangler would have failed on the first crank attempt, but (if ample power existed in the main battery) cranked on the second crank and all those thereafter, turning ESS off in the dash. This is because without a Fuse 42 pull the vehicle could isolate the Aux battery, and determined in lacked sufficient power (which of course it did because it was disconnected.)

 

[THAW]

Your vehicle had no idea the Aux battery was disconnected. There was no detection. It thinks it was still there as there is no check by the vehicle that Fuse 42 was pulled or the Aux battery was disconnected...

Not true. The vehicle detects the changes as evidenced by the 6 ESS event per ignition cycle limit.

 

[UTME]

.

 

[AndySpill]

Not true. The vehicle detects the changes as evidenced by the 6 ESS event per ignition cycle limit.

This comment Foster was said under the context of running the ESS system when switching to one battery, something, if you spent as much time reading as you do looking to find errors in my posts, you’d realize I expressly am against. Several posts up and many places on this forum I recommend turning the ESS system off when bypass

in fact you should know that as you’ve expressly indicated many times against me that doing so in a dual AGM battery JL is ok, while I won’t make that leap.

Without this ESS system engaging your check isn’t happening. I’ve actually never had 6 ESS events in one trip, but that’s beside the point.



Here’s a crazy idea Foster: originate a thread on the forum rather than pathetically waiting in the wings to pedantically pounce that I’m wrong.

I’d be hard pressed to find someone here who contributes as frequently as you but has so little original content to show to his name.

 

[THAW]

Without this ESS system engaging your check isn’t happening.

How do you know the changes aren't recognized on a coud start?

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