Auxiliary Battery Elimination

[mbrose1994]

A number of sources instruct to disconnect the Aux Bat NEG cable end from the Main Bat terminal.
Then to insulate that loose Aux Bat NEG cable end and secure it away from the Main Bat terminals.

Another instruct says "connect the aux battery cable terminal connector to the main battery terminal".

• Is this connecting the POS Aux Bat cable end "in parallel" to the Main Bat POS terminal?

In both cases, what happens when the Aux Bat goes dead?

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[Heimkehr]

Paging @AndySpill

 

[THAW]

Attaching the AUX (ESS) battery positive cable terminal connector to the CR[an]K battery positive post creates a direct electrical path between the CR[an]K battery and the system electronics, bypassing the factory fused and switched connection. Doing so makes the switch state of the PCR (Power Control Relay) and presence/absence of its fuse (F42) irrelevant.

 

[AndySpill]

A number of sources instruct to disconnect the Aux Bat NEG cable end from the Main Bat terminal.
Then to insulate that loose Aux Bat NEG cable end and secure it away from the Main Bat terminals.

Another instruct says "connect the aux battery cable terminal connector to the main battery terminal".

• Is this connecting the POS Aux Bat cable end "in parallel" to the Main Bat POS terminal?

In both cases, what happens when the Aux Bat goes dead?

Hey Michael:

First off, the first option you present doesn't normally represent all the steps recommended to be taken to eliminate the Aux battery, but I'll examine each option, what it does, and what else is required in two separate cases.

In the first situation disconnecting the negative cable that originates at the Aux battery's negative post from the main battery's negative post, and insulating this loose end breaks the circuit to and from the Aux battery. If the Aux battery goes dead, as you inquire about, this cable detachment makes such a dead state of the Aux battery an event that neither effects any other vehicle system, nor is effected by any other vehicle system, as nothing is now connnected to this Aux battery. Restated that Aux battery won't get charged from the alternator with this cable disconnect, nor energize any other vehicle system, not cannibalize the main battery or any other system if it dies. By analogy you are asking me what happens if I connect a wire to only the positive post of a AA battery, and the answer is "absolutely nothing." Power is neither drained from nor supplied to this AA battery, and if it goes dead it effects nothing else.

Because the connection to the Aux battery is broken, and the vehicle wants to see power on the cables normally factory connected to this battery, using this first technique, you have two options (you could do both but you only need to do one) to trick the vehicle into thinking the Aux battery is still there. The first, as @THAW points out is to pull Fuse 42. This prevents the Power Control Relay (PCR) from ever getting energized: which when it does causes the two batteries to be separated, something that normally happens only for an instant at cold crank or during ESS events. The PCR is a normally closed relay that keeps the batteries in parallel but for when its energized.

With Fuse 42 pulled all requests from the vehicle for electrical current, or from the batteries to get charged from the alternator go to all connected batteries all the time, where you have only one battery (the main) connected.

Before @Jebiruph, the father of all this info discovered the Fuse 42 technique, there was the alternative fused jumper between points N1 and N2 in the Power Distribution Center (PDC): you vehicle's intelligent fuse box as detailed here: https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/ This technique, like the Fuse 42 pull, prevents the batteries from being separated as well. If you're curious how, envision the two wires I connect to a light bulb from an energized source. Now, imagine that on the hot (positive) side I add a second wire (the fused jumper between N1 and N2.) By doing this, even if the PCR is energized and breaks the connection on the first hot (positive) wire, there's a second wire (the fused jumper here) to still complete the circuit and conduct electrical current.

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Your second option, taking the positive cable off the Aux battery's positive post and connecting it to the positive post of the main battery is covered by @THAW above. This direct connection to the main battery, unaffected by the state of the PCR, Fuse 42 or a jumpered fuse between N1 and N2 makes the state of Fuse 42 or presence/absence of the jumpered fuse irrelevant: i.e. not wrong to have, nor needed.

Like in the first case you have broken any circuit to the Aux battery, only this time on the positive side of the connection, and the Aux battery, like in the first case neither energizes appliances, nor is energized by the alternator, and its state of charge, if any, is not relevant to another other vehicle system as nothing is connected to it.

Of course in either state you haven't eliminated the Aux battery. It's still there, but nothing connects to it, and it connects to nothing in the form of a completed circuit. You have though , as stated, indeed eliminated its electrical connection to anything in the vehicle: appliances and alternator alike.

 

[mbrose1994]

To @THAW, and @AndySpill,
Many thanks for your posts! Having a good understanding of this Aux Bat situation is very much better than just trying stuff out. As you pointed out, this is an electrical Elimination rather than physical one. Which is perfectly fine and less risk too.
Happy Jeep Trails!

 

[TabarnaCarl]

I took out the aux battery, put the positive wire of the aux battery to the main battery positive, and secure the aux battery negative wire with electrical tape, zip tied it so it doesn't move and that's it. Didn't pull any fuse. ESS still work perfectly, but I have disabled it with my tazer mini.

Just a tip ; it is wayyyy more easy to access the aux battery from the passenger side inner fender. Took the inner fender out, and there is 3 10mm bolt to take out and you have access to the aux battery.

 

[mbrose1994]

[@TabarnaCarl] post
Makes sense.
But the videos (YouTube) I've seen so far show taking off the RF wheel and fender to get the liner off.

And the fender has an electrical plug to disconnect while the liner is still attached. Then dropping the battery case includes awkward wrench work to detach both cables from the dangling Aux Bat.

Then, I guess, the loose cable ends must be taped up and left loose in the reattached battery case? And must buy new clips in advance to replace those broken taking off the fender.

The whole fender process is a lot. Not sure of value for the effort.

 

[TabarnaCarl]

[@TabarnaCarl] post
Makes sense.
But the videos (YouTube) I've seen so far show taking off the RF wheel and fender to get the liner off.

And the fender has an electrical plug to disconnect while the liner is still attached. Then dropping the battery case includes awkward wrench work to detach both cables from the dangling Aux Bat.

Then, I guess, the loose cable ends must be taped up and left loose in the reattached battery case? And must buy new clips in advance to replace those broken taking off the fender.

The whole fender process is a lot. Not sure of value for the effort.

I did not took the fender off, neither the wheel, just turned full steer to the right. And yeah, when unbolting the bottom tray of the battery, the aux battery will hang by its wire. Just have to support it with one hand and unbolt the 10mm from both terminals. It's kinda awkward but it's pretty easy.

The inner fender is also pretty easy to take off. Broke the rivets with a prybar, or drill through them and they will fall off. And there's 2 or 3 10mm bolt, that's it.
If you don't have a rivet gun to put back the inner fender, you can put like christmas tree plugs (I don't know how they're called in English lol).

 

[Heimkehr]

Just a tip ; it is wayyyy more easy to access the aux battery from the passenger side inner fender. Took the inner fender out, and there is 3 10mm bolt to take out and you have access to the aux battery.

That is in fact the recommended method. It allows the owner to avoid disturbing the PDC, which is always a good thing.

 

[mbrose1994]

Success, 90% level. Did the 2 most straight forward, least OEM modifying steps.

• Disconnected the AUX batt NEG cable end at the Primary batt.
• NOTE: On my JLU Sahara 2018, the AUX batt NEG cable end was attached to the extra post on the Primary batt NEG cable end. Beware, a YouTube video shows exactly opposite.
• Pulled F42 in fuse box.

The 10% NOT success is my center dash behind the steering wheel shows the ESS disable warning symbol. It is immediately above the top of the fuel level bar. The actual ESS button switch on the center console appears to work as normal. Start up is OFF, during run time pushing the button switch turns button indicator light ON. And second push turn button indicator light OFF.

The 90% SUCCESS is the ESS is disabled at start up and remains so. And the Dash Screen that shows the ESS system reports the ESS system is disabled or OFF.

So, not sure what pulling the F42 fuse actually does.
I could re-seat the F42 fuse and have the same result?

 

[Ravenbane†††]

I'm a little confused...

1. Why remove an aux battery?
2. What vehicle(s) are being discussed here?

 

[mbrose1994]

I'm a little confused...

1. Why remove an aux battery?
2. What vehicle(s) are being discussed here?

Began discussion on my 2018 JLU Sahara. Saw a number of issues and discussions centered on AUX battery and ESS. I see no value in AUX batt long term. Result was best way to remove or eliminate it. And now have good result.

 

[AndySpill]

I'm a little confused...

1. Why remove an aux battery?
2. What vehicle(s) are being discussed here?

Shane..and I mean no disrespect, your question, on a forum like this, is a little bit like taking a trip to NYC today and asking, "wait, what happened to the twin towers?"

I say this because one would be hard pressed to find a topic more discussed here, but I'll bite.

Several, but not all implementations of the JL Wrangler are equipped with two AGM (absorbent glass mat: a type of lead acid battery capable of delivery and recouping charge well, as needed in engine start stop (ESS) events) batteries, a main and a smaller Aux.

When such vehicles enter ESS events they're appliances are normally energized by the Aux battery, preserving the main for engine cranking. Many vehicles run ESS on one battery. Stellantis decided upon two, some say because the vehicle electronics were too voltage sensitive.

These two dissimilar sized batteries are always in parallel but for an instant when you crank, to test the Aux battery, and during these ESS events. This parallel connection can allow one battery to take out the other if it goes bad, as forum members have reported the Aux to do from time to time to the main battery.

So given the hatred of ESS events by many owners, coupled with the cannibalistic nature of this Aux battery, many owners have chosen to disconnect this Aux battery and take the additional but simple steps into tricking the vehicle into thinking that the Aux battery is still connected, so as to avoid diagnostic error conditions that might arise if the vehicle detects the absence of this Aux battery, along with turning ESS off, either by pressing the button on the console or buying tech that does this for them.

 

[mbrose1994]

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.

 

[Cartman]

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.

sorry I do not get it. do you have soiime pictures?
which 2 +? discvonnect?
What is CRK?
What is N2 vs N1?

I just disconnect and isolate negative cable that have infinit Ohms to ground when the both negative cables was dissconnected. also I remove fuse 42 and it seems everything works.
BUT till now ASS never worked and now its working....

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