Another battery question{sorry]

[tony58]

I have a 2024 2 door Rubicon, I switch off the ess switch when I drive the jeep. My question is should I still pull the f34 fuse and disconnect the negative battery going down to the aux battery?I do not want to drain the main battery, also if I need to jump start the jeep, do you just jump it the same way without the aux battery, thanks this site is great!!!!

Sponsored

 

[AndySpill]

I have a 2024 2 door Rubicon, I switch off the ess switch when I drive the jeep. My question is should I still pull the f34 fuse and disconnect the negative battery going down to the aux battery?I do not want to drain the main battery, also if I need to jump start the jeep, do you just jump it the same way without the aux battery, thanks this site is great!!!!

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.

 

[AndySpill]

Edit: I probably should have expressed ways to determine if owners have a dual AGM battery JL. It's my understanding that those JLs that don't (e.g. Etorq, 4xe) won't have a Fuse 42 plugged into the #42 slot, and only one factory cable on the main battery's negative terminal.

More, that fuse in in the Power Distribution Center (PCR) a black box near the passenger's compartment near top under the hood, on dual AGM battery JLs. I want to say that I heard that the position of this box is more forward in the engine bay in non dual AGM battery JLs.

Someone else can confirm that I hope.

 

[MrMischief]

Nice info. The other day I had a question on here about this and its impact due to a dead main battery just before a long drive. Well now that I'm where I need to be I decided to hook the smaller battery back up and reinstall the fuse then go for a drive. What I noticed was that the voltmeter was reading ~14.4 volts and ESS was functioning. After about a 15 minute drive I parked for about two hours. When I returned to the Jeep it started without issue and as I drove I noticed that the smart alternator seemed to be fluctuating the voltage, it would read about 12.8 volts while driving but when coasting that would jump to ~14.4 volts. This is the same voltage behavior I saw when the smaller battery was disconnected and I believe it is normal behavior. So now I'm wondering... Is this indicating that the smaller battery is fine? Can I trust it to continue to be fine? And if I want to keep the smaller battery isolated, what is the best product to wrap the extra negative battery cable in? I had just wrapped it well with electrical tape and zip tied it up out of the way, it survived about a 500 mile drive at 80 mph just fine, but I wonder if that tape will melt on a hot day crawling in four low where the under hood temps can get quite high. I like the idea of being able to easily put it back to factory if I ever need to have a dealer look at it so they don't just say "you had a loose cable and a missing fuse, that's why your axle broke"

 

[Yawnie'sPapa]

Nice info. The other day I had a question on here about this and its impact due to a dead main battery just before a long drive. Well now that I'm where I need to be I decided to hook the smaller battery back up and reinstall the fuse then go for a drive. What I noticed was that the voltmeter was reading ~14.4 volts and ESS was functioning. After about a 15 minute drive I parked for about two hours. When I returned to the Jeep it started without issue and as I drove I noticed that the smart alternator seemed to be fluctuating the voltage, it would read about 12.8 volts while driving but when coasting that would jump to ~14.4 volts. This is the same voltage behavior I saw when the smaller battery was disconnected and I believe it is normal behavior. So now I'm wondering... Is this indicating that the smaller battery is fine? Can I trust it to continue to be fine? And if I want to keep the smaller battery isolated, what is the best product to wrap the extra negative battery cable in? I had just wrapped it well with electrical tape and zip tied it up out of the way, it survived about a 500 mile drive at 80 mph just fine, but I wonder if that tape will melt on a hot day crawling in four low where the under hood temps can get quite high. I like the idea of being able to easily put it back to factory if I ever need to have a dealer look at it so they don't just say "you had a loose cable and a missing fuse, that's why your axle broke"

Voltage displayed will fluctuate between about 12.6 up to 15.0 - depending on battery temperature, battery SoC (state of charge), system load and more.
12.8 indicates the battery/batteries were fully charged and there was no real need to push anything into them. Coasting the system saw the torque of the engine drop so figured to top the batteries up when there was no torque demand.
Totally 100% normal and it doesn't matter a lick if the aux battery is there or not because the IBS ONLY senses the crank or main battery health, temperature, and the amp hours coming out vs. amp hours going in.
Further - many of us on the Gladiator side have proven that it's almost as likely for the main battery to fail first. Some have seen battery failure, replaced the main and gotten another year out of the aux battery.
there's a whole lot of misinformation out there.
When a battery fails, there's many ways it can fail -and a dead battery isn't proof that it will kill the second battery. It may, but it may not. The main may fail and kill the aux - it may, or it may not drain the aux.

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.

It's not "take effect" it's overcoming the draw of a dead battery that pulls from the jump pack, or the donor/host vehicle you are jumping from.
It's the same rules that have applied since I first got into automotive electric systems (in which I specialized for about 50 years).
If the battery is "dead", then power from a pack or other vehicle will have to raise the voltage of the dead battery enough to have power to then crank and start the dead vehicle.
Too often people clamp on, jump in and try to start - FAIL.
Even older vehicles can be that way - with a single battery and no ESS. There have been times where I've needed to connect cables, sit in my running vehicle, IDLE UP! and wait a couple of minutes or so - this put enough into the dead battery that it was no longer dropping the voltage at the dead vehicle's systems and it would start.

So it can happen multiple ways:
aux battery dies, doesn't kill main battery,
aux batteries dies, is a drain on the main battery (and depending on things, won't necessarily ruin the other battery - it just takes some doing and a good charger to fix it)
main battery dies, doesn't kill aux battery
main battery dies, drains aux battery
You can generally jump if you have a hefty enough jump pack or your running vehicle is idled up to push back into the dead or very low battery - if you take a few minutes.
Frankly, using my methods, I've never had a failure in jump starting a dead vehicle, including Jeeps.
Idling up the donor vehicle, sitting for a few minutes, THEN trying will often work.

Me - I've enough electrical experience and watch things closely enough - I have no fear of not being able to jump a vehicle so my Jeeps get left alone - ESS and aux battery untouched.
If things get to looking wonky on system voltages and so on, I may isolate the two batteries, do a full proper AGM charge going through all phases, and rest the IBS and move forward once again with no troubles.

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.

Not sure where that comes from - the PCR isolates the aux battery only a brief moment for a check.
How can it "seek to use only the main battery" ? They are in parallel only when the PCR is closed and isolated only for a brief time when the voltage check is done.
The main battery isn't connected directly to N1. the aux battery is always connected to N1.
only the main battery is connected to the starter directly. When the PCR is closed, there may be a small bit of current from the aux battery for cranking, but it's going through a relay and smaller wiring, not going to aid much at all, and if it did, then the drop in voltage due to cranking would kill voltage to N1.

Would like to see how that is drawn out electrically, a schematic.


A proper jump sequence, and allowing a running vehicle to charge the batteries a bit before attempting to start the dead Jeep will start almost anything.

 

[Heimkehr]

...if I want to keep the smaller battery isolated, what is the best product to wrap the extra negative battery cable in? I had just wrapped it well with electrical tape and zip tied it up out of the way, it survived about a 500 mile drive at 80 mph just fine, but I wonder if that tape will melt on a hot day crawling in four low where the under hood temps can get quite high.

I've used Scotch Super 88 electrical tape to good effect for many years on motorcycles, where its [necessary] proximity to hot engine parts tested/confirmed its robustness over time. Just a suggestion. I do occasionally use a quality, temperature-rated wire loom in conjunction with the tape, for additional protection.

Yes, for the sake of safety, do put as much distance between the wrapped part(s) and the engine block as you're able to do.

...the IBS ONLY senses the crank or main battery health, temperature, and the amp hours coming out vs. amp hours going in.

With respect, Bill, are you sure about that? The IBS is connected to the main battery's Negative terminal, above which the corresponding cables for both batteries (main & ESS) are secured and, as pictured, routed through the IBS. How would the IBS physically segregate and thus report on just the health of the main battery?

 

[tony58]

Andy ,Yes you are correct I do not have etorq or 4xe so all I need to do is pull fuse 42 and take negative cable off aux battery and tape it up and I should be good to go without any damage to anything, jeep has only 400 miles but do not need ess.

 

[THAW]

Voltage displayed will fluctuate between about 12.6 up to 15.0

My understanding is it maxes at 14.4V. Is that not correct? What's the source for the 15.0 figure?

 

[THAW]

The IBS is connected to the main battery's Negative terminal, above which the corresponding cables for both batteries (main & ESS) are secured and, as pictured, routed through the IBS. How would the IBS physically segregate and thus report on just the health of the main battery?

At first, I had the same thought. But, doesn't the return path for the ESS battery pass through the cables to the ESS negative terminal (i.e. "over" the IBS)?

 

[Heimkehr]

At first, I had the same thought. But, doesn't the return path for the ESS battery pass through the cables to the ESS negative terminal (i.e. "over" the IBS)?

My question stems from the physical installation of the IBS evident on our vehicles. If there's intelligence, so to speak, that it uses to segregate batteries for reporting purposes, etc., that's the intel that's being sought.

 

[TheNewGuy]

My understanding is it maxes at 14.4V. Is that not correct? What's the source for the 15.0 figure?

I've seen mine go as high as 14.7

 

[THAW]

I've seen mine go as high as 14.7

Interesting. There's a label on my OE AGM main battery stating "limit charge volts to 14.4"

 

[TheNewGuy]

Interesting. There's a label on my OE AGM main battery stating "limit charge volts to 14.4"

?‍

 

[THAW]

My question stems from the physical installation of the IBS evident on our vehicles. If there's intelligence, so to speak, that it uses to segregate batteries for reporting purposes, etc., that's the intel that's being sought.

Since the IBS sits between the ground wires and the negative terminal of the main battery, I believe it can measure current in/out of the main battery only (not the ESS battery, to Bill's point).

The IBS could, however, measure voltage both when the ESS battery is connected and disconnected - and the data could be used to infer information about ESS battery voltage. If it has a switched power connection to N1, it could measure the ESS battery voltage directly.

 

[THAW]

?‍

Sponsored