3.6L ESS Dual Battery Consolidated Information

ALRUI

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Just replaced both of ours at 40K miles, quick how to here:





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rbranst

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First - thanks to Jebiruph for this thorough thread. I can't see digging into an ESS issue without referring to this first. I wanted to pass my story along.
I encountered a dead battery and had to be jumped and thought it was a fluke. I got home and started the car back up just to make sure I was good. Next morning, battery was dead. I left the JL at home and drove another car. I picked up a brand new Optima DH6 on the way home from work that night and put it in. Car was still dead. It was at this point I began learning about the aux battery and realized I probably needed to replace that one too. Once I did this, the car would start again but it would never engage ESS and always gave me errors about either "Battery Charging" or "Battery Protection Mode". In the process of investigating all of this, I trickle charged for a day, but it made no difference. Aux battery voltage was fine, but main was 10.5-11 on the new Optima! I discovered the negative lead to the aux was corroded at the main battery Neg terminal. I cleaned it really good, trickle charged again and now my start stop worked briefly. Finally after a few days I began to suspect my main battery, it was always at 10.5V after long drives. I returned the Optima DH6 for a replacement. Once installed and the terminals lubricated everything works perfectly.
The overcomplicated system actually hid bad brand new battery! That's the one thing I would like everyone to get from this post. The Aux was definitely bad, but the bad main replacement I got really screwed up my troubleshooting. I was looking at alternator voltage, considering a battery sensor replacement, bad wiring harness, etc. Never considered a brand new Optima being bad!
 

ALRUI

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Never considered a brand new Optima being bad!
Bad Optima is horrible, I thought those were supposed to be awesome. Had it been sitting on the shelf for a long time?
 

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Due to the quantity and length of ESS battery and electrical related threads, researching issues can be time consuming and confusing. I am using this post to make information and related links easily available. This first post will serve as a quick reference and I'll use the second post to provide more details.

JL Wranglers with the 3.6L ESS have 2 batteries, the Main battery that you see in the engine compartment and an Aux battery that is hidden underneath the Power Distribution Center. Each battery powers separate systems during an ESS auto stop. During normal operation, the batteries are connected together in parallel by the Power Control Relay.

JL Wranglers are jump-started just like any other vehicle, except with two batteries it will take more time/power.

On a properly operating system, the batteries are always connected in parallel through the PCR except during an ESS auto stop.

The batteries can go bad independently, but they will run down (or drain) together. Except when a bad battery relay (PCR) or or a blown PCR (ESS) fuse separates them, which will also prevent the Aux battery from charging.

My battery is dead and I can't jump start my jeep
On a properly functioning system the batteries go dead together, so to jump-start a JL you have to overcome two dead batteries. Compared to a single battery system, it will take more time/power to over come two dead batteries. Disconnecting the main battery and jump-starting with just the aux battery should be easier.

My dash is flashing on and off and I can't jump start my jeep
This condition seems to be caused when the Aux battery can provide some, but not adequate power to system electronics, either because it is bad or partially drained. A bad aux battery should be bypassed using a jumper or by unplugging the PCR. Partially drained means either both batteries are drained, or the aux battery is isolated (bad PCR or PCR fuse) and not getting charged. If only the aux is drained, bypassing it with a jumper or unplugging the PCR may be enough to get started, but a jump-start may still be needed. If both batteries are drained, a normal jump-start (more time/power) should be enough.

Bypassing the Aux Battery
A bad or discharged aux battery can affect PCR operation, which can be disruptive to system electronics and it may need to be bypassed. Bypassing can be accomplished by using a (fused) jumper wire to connect the main battery directly to the system electronics at PDC terminal N1 or by unplugging the PCR, preventing it from disrupting the system electronics.

Using the Aux Battery as a Dedicated Reserve Battery
A good aux battery can be bypassed and disconnected from the system (by removing the ground cable) to be held in reserve in case the main battery is not able to power a start. A dead main battery should be disconnected from the system before attempting to start from the reconnected aux battery. The aux battery should also be load tested and fully charged before relying on it as a dedicated reserve battery.

Links to Related ESS Information
(added descriptions to links 05/12/19)
3.6L ESS Battery Diagram
This thread started it all. Due to various conflicting information regarding the dual battery wiring, I made this basic diagram based on information available online.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-diagram.14401/

3.6L ESS Aux Battery Bypass
An Aux battery bypass lets you start/run with just the Main battery. Handy if the Aux battery is bad or you want to disconnect it to use as a reserve battery.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

3.6L ESS Battery Basics
Here is some basic electrical theory to explain the dual battery system and why it can be difficult to start with a portable battery booster.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-basics.20794/

3.6L ESS IBS Information
This thread provides information about the Intelligent Battery Sensor that monitors the health of the Main battery. It's this type of sensor that makes ESS systems possible by analyzing the ability of the battery to restart from an auto stop.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-ibs-information.22585/

3.6L ESS Battery Basic Load Testing (Battery Health Check)
If you're concerned about the condition of your batteries, here's how to check them with a cheap load tester.
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-basic-load-testing.22031/

3.6L ESS Cold Start (added 4/26/19)
Why is the Aux battery so critical to the cold start process? (Critical, but unnecessarily so?)
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-cold-start.28297/
 

WranglerMan

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Bad Optima is horrible, I thought those were supposed to be awesome. Had it been sitting on the shelf for a long time?
Optima batteries have gone down hill over the years, not even close to the quality they used to be.....Better off with Odyssey, Northstar, Full River
 
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Jebiruph

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  • Thread starter
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First - thanks to Jebiruph for this thorough thread. I can't see digging into an ESS issue without referring to this first. I wanted to pass my story along.
I encountered a dead battery and had to be jumped and thought it was a fluke. I got home and started the car back up just to make sure I was good. Next morning, battery was dead. I left the JL at home and drove another car. I picked up a brand new Optima DH6 on the way home from work that night and put it in. Car was still dead. It was at this point I began learning about the aux battery and realized I probably needed to replace that one too. Once I did this, the car would start again but it would never engage ESS and always gave me errors about either "Battery Charging" or "Battery Protection Mode". In the process of investigating all of this, I trickle charged for a day, but it made no difference. Aux battery voltage was fine, but main was 10.5-11 on the new Optima! I discovered the negative lead to the aux was corroded at the main battery Neg terminal. I cleaned it really good, trickle charged again and now my start stop worked briefly. Finally after a few days I began to suspect my main battery, it was always at 10.5V after long drives. I returned the Optima DH6 for a replacement. Once installed and the terminals lubricated everything works perfectly.
The overcomplicated system actually hid bad brand new battery! That's the one thing I would like everyone to get from this post. The Aux was definitely bad, but the bad main replacement I got really screwed up my troubleshooting. I was looking at alternator voltage, considering a battery sensor replacement, bad wiring harness, etc. Never considered a brand new Optima being bad!
Thanks for posting. I don't think the aux battery causes anywhere near the issues it gets credit for. After 3 years, my main needed replaced, but the aux is still good. It is part of an overly complicated system prone to failure, but it's usually not impossible to trouble shoot with the diagram and a volt meter. It's not like it's death wobble or something like that.
 

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Forgive me if this is dumb, but...

My 2019 Sport with 3.6 (7000 miles on the clock...I 0nly drive it about once a week) has been reading "ESS Unavailable, Battery Charging" for at least 4 months. Vehicle always starts, even at -30 F, and main battery gauge reads 14.3 consistently. Dealership says bring it in overnight, warranty work. Rather not.

Given that I never use the ESS, do I really need to do anything? Is the aux maybe flat just because I dont drive enough?
 

WranglerMan

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Forgive me if this is dumb, but...

My 2019 Sport with 3.6 (7000 miles on the clock...I 0nly drive it about once a week) has been reading "ESS Unavailable, Battery Charging" for at least 4 months. Vehicle always starts, even at -30 F, and main battery gauge reads 14.3 consistently. Dealership says bring it in overnight, warranty work. Rather not.

Given that I never use the ESS, do I really need to do anything? Is the aux maybe flat just because I dont drive enough?
Could be a combination of not driving a lot and a bad battery, my suggestion is to get a smart charger of good quality like NOCO, CTEK or similar and charge it up and see if the issue gets resolved.
 

OldGuyNewJeep

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Forgive me if this is dumb, but...

My 2019 Sport with 3.6 (7000 miles on the clock...I 0nly drive it about once a week) has been reading "ESS Unavailable, Battery Charging" for at least 4 months. Vehicle always starts, even at -30 F, and main battery gauge reads 14.3 consistently. Dealership says bring it in overnight, warranty work. Rather not.

Given that I never use the ESS, do I really need to do anything? Is the aux maybe flat just because I dont drive enough?
That “gauge” is showing you how many volts the alternator is sending to charge the batteries, not how many volts the batteries have. The higher the number, the more depleted they are.

If you have a multimeter, disconnect the aux negative and test voltage of both main and aux, separately.

A quick easy test is to put Jeep in ACC mode and look at the voltage shown on EVIC. That is a more accurate picture of current voltage.

Lastly, but most importantly, buy a battery tender and use it weekly. Infrequent, short trips are a recipe for failure with this crappy dual battery setup.
 

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