Another battery question{sorry]

[VJT]

I'm going to assume Tony that your Rubicon is one equipped with dual AGM type batteries. If not, the following won't apply.

If you have resolved to turning off the ESS system, either by pressing the ESS button after each cold crank, or buying aftermarket tech to do it for you, there is, in my opinion, little benefit, and potential problems keeping the ESS/Aux battery within the electrical connections of the vehicle.

A fair enough number of owners have had these ESS/Aux batteries not only fail on them, but in their parallel connection to the main battery, cannibalize the main battery as well.

Accordingly, given that you've already resolved to not using the ESS system (my answer would be different if you wanted to have ESS events) I recommend that you disconnect the ESS/Aux battery by identifying the black cable on the main battery's negative post that does NOT have as its other end the body ground on the passenger's front quarter panel just under the hood.

The other cable, which you should disconnect at the main battery's negative terminal, and wrap insulative material around its loose end, has as its distal connection the negative post of the ESS/Aux battery.

The prior two paragraphs were carefully worded by design as the two cables in question swapped their position on the main battery's negative terminal, I am to understand, sometime in 2021. My instructions apply to all model year dual AGM battery JLs.

This cable disconnection action will take the ESS/Aux battery out of the electrical schematic of the vehicle.

In concert with this action I recommend that you pull Fuse 42, not Fuse 34 as you've described. This action prevents the Power Control Relay (PCR) from being energized, which when it's in such an energized state isolates the two batteries.

Pulling this fuse means that calls by the vehicle to isolate the ESS/Aux battery will silently fail, and power will instead come from all available batteries, for which you will just be the main battery, given your disconnection from the ESS/Aux battery as described in the above cable pull step.

Nothing changes about jump starting procedure, just timing; I'll explain. If you need to jump start you should place your cable's positive on the battery failing JL's main battery positive, then the charge source's positive, then the charge source's negative and then some body ground point on the battery failing JL.

You will not need to wait as long for this connection to "take effect" as if you had the ESS/Aux battery connected, and as the owner's manual describes.

Let me try to explain that. In dual AGM battery JLs, when you attempt to cold crank they attempt tp isolate the ESS/Aux battery to test it for voltage prior to the engine crank. If this battery lacks adequate voltage the original 2018 JLs will be "dead in the water." Later model JLs, on the second crank attempt, seek to use only the main battery and if successful continue on future cranks to use the main battery only until, if ever, an energized ESS battery is reintroduced.

But if you pull Fuse 42 that attempt to isolate the ESS/Aux battery will instead be routed to the main battery: the same battery the jumper cables are directly connected to. So jump starting, after the changes I describe, will be much like that for "your father's Oldsmobile."

Final thought: if you take these steps please avoid running ESS events. While many vehciles do run ESS events with one battery, and you probably will be fine if you forget, the perfect storm of an "on its way out" main, battery, a cold night, too many aftermarket appliances drawing current, and a long red traffic light could find the vehicle early terminating the ESS event due to drops in voltage of your main battery, too late for that battery to have ample voltage to effect the engine recrank.

By the above instructions, is it that easy to disconnect the ESS: disconnecting black wire and pulling fuse 42? If so, why do people pay for an instrument (approx. $100.00) to terminate the ESS? Is there any adviser reaction from the wire disconnect and fuse pull?

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[AndySpill]

By the above instructions, is it that easy to disconnect the ESS: disconnecting black wire and pulling fuse 42? If so, why do people pay for an instrument (approx. $100.00) to terminate the ESS? Is there any adviser reaction from the wire disconnect and fuse pull?

The reason Vic that people pay for tech to terminate the ESS system is convenience.

I am all but certain that doesn't fully answer your question so I'll elaborate.

The disconnecting of the ESS battery, along with pulling Fuse 42, by design, does not disconnect the ESS system. The system and the battery are two different things.

In fact it is the process of pulling Fuse 42 that tricks your dual AGM battery JL into thinking that it still has its ESS battery. When it does voltage checks of what it thinks is only the ESS battery it thinks it's isolated, to determine whether it is okay to engage the ESS system, those checks, as a result of the fuse pull and ESS battery disconnect are effected against only the main battery.

As a generaly rule it's probably best not to run the ESS system with one battery, so people turn it off, sometimes buying tech to do it for them. Lots of vehciles run ESS with one battery but those same vehicles after dont' have the aftermarket electrical current drawing appliances that JLs do. In the perfect storm of an on its way out main battery, a cold night, a long trafffic light and too many appliances running, the ESS system can early terminate due to a battery voltage drop, perhaps not in time for the one battery to have adequate charge to crank the battery. We don't worry about this with the factory ESS setup because the main battery is isolated during ESS events precisely so it has the power to effect the bulk of the post ESS event engine crank.

Fuse 42, when inserted, powers the Power Control Relay (PCR) that temporarily separates the two batteries for an instant at cold crank and during ESS events.

Without that fuse the PCR can't energize, the batteries can't separate, and calls for current from only the ESS battery now go to all batteries, of which, as result of your disconnecting the cable to the ESS battery is just now the main battery. The vehicle's computer is not aware of the no longer functioning PCR. It thinks it got its voltage reading from the ESS battery when in fact, as a result of your two changes (cable pull, fuse pull) the reading was from the main battery.

I think you've asked what dealers think about this change. My guess is most don't care. For those that do I'd advise charging the ESS battery first, the reconnecting the cable and fuse before service.

To charge only the ESS battery your charger's positive side should be placed on the main (that's right, I said main) battery's positive terminal and the negative side of the charger on the dangling cable you disconnected and whose end you have temporarily uninsulated for this exercise. As the main battery's positive is connected to the ESS battery's positive (in fact your pulling Fuse 42 makes this always the case) the only closed circuit your charger has made here is with the ESS battery.

Make sure to reinsulate that dangling cable when done charging.

I hope that helps and makes sense.

 

[THAW]

Then you reference thoughts on how--if I've got this right--difference in the state charge between two AGM batteries about to be brought into parallel, just like those batteries of many JLs after an ESS event, more than those batteries' diffferent capacities, is the more critical factor.

Ok. So wouldn't that suggest running ESS events with all batteries, different from the Stellantis design that you like, so they can discharge together, be better for the batteries?

Andy, I don't think SOC differential indicates single power source ESS system design; all good engineering designs have tradeoffs. And, I agree with you: a dual battery system is mostly superior (since it's less likely to strand drivers).

But, imagine if the 12Ah ESS battery were located in the open engine bay, in the battery tray next to the main battery...

ESS light on? Prescription: open the hood and replace the battery in well under 5 minutes labor with a wrench and scredriver for slightly more than $100 part cost; don't put it off or you'll create problems! It could be done at Jiffy Lube.

ESS light not on? Replace the battery at every 20k service interval.

There'd be little need for discussion of cables, fuses, battery sizes, parallel charging, etc. That's my point about the good design and its actual primary flaw.

the costs you cite of perhaps alternatively running them down in equal amounts in an ESS event to preserve their life

I did not suggest running the batteries SOC down equally. Attempting to do so doesn't make sense. I am not suggesting ways to create optimal charging, which does not and will not happen with an alternator. My point is the exact opposite: charging based partial fixes are not a good overall solution.

If your point was to show the limitations of A.I. I agree. I don't post a link (mine) I don't first read and agree with.

I am not interested in discussing AI on this forum, but I concur.

I think about what AI tools would have recommended for peanut consumption in infants in the not too distant past, and wonder how long it would've taken new data to overwhelm the outdated.

 

[zouch]

pity, isn't it, that Stella didn't set up all JL(U)s Aux batts the way the did for the Diesels?
the Aux Batt on a Diesel is easily accessed via a trap door under the main batt; no disassembly of anything required.

If I may, I agree that replacement of the ESS/Aux battery through the side, although the Stellantis service advised procedure, probably wasn't part of the original vehicle specs until the frequency of this change necessitated a procedure that statistically would cost less than going in from the top and a service tech risking damage of expensive PDC components in the process. bjut I find it hard to believe a procedure that has the potential to rip apart plastic rivets, as cheap as they are to replace, was the intended way to replace the battery from the vehcile's original design.

But now with this procedure in place, it really isn't that hard to replace the ESS battery.

 

[jeepoch]

It amazes me to no end all the amazingly detailed effort to electrically fix a bureaucratic problem. The fix is NOT where everyone is dealing with it.

Why are you all spending way so much effort, energy and frustration to fix something that should never have been put there to begin with?

Argh... Please start fixing the root cause than coming up with such complicated insignificant 'under-the-hood' band aids!!!

It should be plainly obvious where the problem truly lies.

Jay

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