ESS Dual Battery System Operation

[jebiruph]

We've been hashing out the ESS dual battery system for a few years over on the JL forum and I think we have it fairly well sorted. Not all JT owners visit the JL forum, so I thought I'd start this post here for discussing how it works and it's various issues.

As an overview, the system consists of a small aux battery to power the interior electronics during an auto stop, conserving the main battery power for restarting. There is a PCR (Power Control Relay) that separates the aux battery and interior electronics from the main battery and engine electronics during an auto stop. The PCR is a normally closed relay, meaning when no power is applied, the relay terminals are connected. There is an IBS (Intelligent Battery Sensor) that monitors the electrical current into and out of the main battery and reports the main battery's state of charge and state of health to the ESS system. The aux battery is not monitored, instead the PCR is briefly activated during a cold start to separate the systems for quick aux battery test. If the aux battery fails the test, the auto stop/start throws an error and is disabled.

This first diagram shows the ESS related components and battery cables in their relative positions under the hood. Note that the negative cables at the main battery were switched at some point.

This diagram shows that when not auto stopped, both batteries are connected to everything. Since the batteries are connected to each other most of the time, if one goes bad, it can drain and impact the health of the other battery.

This diagram show how the electrical systems are separated during an auto stop.

This diagram shows that with the positive and negative terminals separated from the main battery, the aux battery is still connected the positive terminal. If the positive terminal gets shorted to ground, it will blow the high capacity fuse connected to the N3 terminal, separating the aux battery and interior electronics from the rest of the system.

With the high capacity fuse at N3 blown, the aux battery and system electronics are isolated from the alternator and the main battery. The aux battery becomes the only source of power for the system electronics and it is not getting charged from the alternator. Eventually the aux battery will run down and no power will be available to the system electronics, disabling the vehicle. At this point, attempting to jumpstart the main battery won't help because power will still not get to the system electronics.

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[Alans17]

We've been hashing out the ESS dual battery system for a few years over on the JL forum and I think we have it fairly well sorted. Not all JT owners visit the JL forum, so I thought I'd start this post here for discussing the how it works and it's various issues.

As an overview, the system consists of a small aux battery to power the interior electronics during an auto stop, conserving the main battery power for restarting. There is a PCR (Power Control Relay) that separates the aux battery and interior electronics from the main battery and engine electronics during an auto stop. The PCR is a normally closed relay, meaning when no power is applied, the relay terminals are connected. There is an IBS (Intelligent Battery Sensor) that monitors the electrical current into and out of the main battery and reports the main battery's state of charge and state of health to the ESS system. The aux battery is not monitored, instead the PCR is briefly activated during a cold start to separate the systems for quick aux battery test. If the aux battery fails the test, the auto stop/start throws an error and is disabled.

This first diagram shows the ESS related components and battery cables in their relative positions under the hood. Note that the negative cables at the main battery were switched at some point.

This diagram shows that when not auto stopped, both batteries are connected to everything. Since the batteries are connected to each other most of the time, if one goes bad, it can drain and impact the health of the other battery.

This diagram show how the electrical systems are separated during an auto stop.

This diagram shows that with the positive and negative terminals separated from the main battery, the aux battery is still connected the positive terminal. If the positive terminal gets shorted to ground, it will blow the high capacity fuse connected to the N3 terminal, separating the aux battery and interior electronics from the rest of the system.

With the high capacity fuse at N3 blown, separating the aux battery and interior electronics from the rest of the systems, the aux battery will not be getting charged from the alternator. Eventually the aux battery will run down and no power will be available to the interior electronics, disabling the vehicle. At this point, attempting to jumpstart the main battery won't help because power will still not get to the interior electronics.

Greatly appreciate the thorough write up! I was just studying up on this, today. I’ll need to read through again to really digest everything.

Had anyone discovered a way to make this a poor man’s Genesis dual battery setup?

 

[ShadowsPapa]

Two things, one is a question:

1. My wife's 2018 WK2 got to the point the ESS stopped working. She didn't really notice it as a lot of her drives are short enough (30 minutes or less) that on some trips it didn't stop anyway. And she never toggled through to see the status.
Eventually it got to the point her Jeep didn't start after sitting a few days. I'd jump start it and away she went. It was fine for a few days, then would act like a dead battery again. Jump start it and it was ok. Then finally I decided to run my charger on it for 24 hours then check the voltage after charging. Should be 12.6 if all is well. It wasn't. It showed about 11.x when measured at the top/main battery. Took it to dealer, they said both batteries were bad, replaced them both under warranty and life was good (until she traded it weeks later).
Point - the aux battery went bad and eventually took out the main battery to the point it wouldn't hold a charge very long. Dealer said both tested bad.
That fits your description.

2. My JT often doesn't do the ESS thing - I toggle to the ESS page and it says "not ready, battery charging". If it doesn't check the aux battery - how does it know that?
I can drive it for 30+ minutes and it still doesn't work. I've driven it 45 minutes, checked, and it still says "battery charging". Then maybe I'll park for half an hour, come back out and it works.
Then sometimes it won't work, it will say battery charging, then after another 10 minutes of driving, at the next stop - it works. If it doesn't check that aux battery while driving - how does it know the status and suddenly start working? I can get that not read message even if the JT has sat for only 12-18 hours - can't be THAT low. And yet today we drove it for more errands and it worked after only a few minutes/miles, when the truck was warmed up, it worked fine.
It must monitor somehow to know the battery situation as to say not ready battery charging then start working without shutting off and starting again.
Can't be the main battery because the volt meter on the dash says it's running pretty high voltage (these things run higher voltages than anything I've ever owned - if I saw this type of running voltage on my other vehicles I'd say the regulator was shot and over-charging)

 

[jebiruph]

Greatly appreciate the thorough write up! I was just studying up on this, today. I’ll need to read through again to really digest everything.

Had anyone discovered a way to make this a poor man’s Genesis dual battery setup?

Try this thread https://www.jlwranglerforums.com/forum/threads/ess-dual-battery-management.60034/

 

[jebiruph]

Two things, one is a question:

1. My wife's 2018 WK2 got to the point the ESS stopped working. She didn't really notice it as a lot of her drives are short enough (30 minutes or less) that on some trips it didn't stop anyway. And she never toggled through to see the status.
Eventually it got to the point her Jeep didn't start after sitting a few days. I'd jump start it and away she went. It was fine for a few days, then would act like a dead battery again. Jump start it and it was ok. Then finally I decided to run my charger on it for 24 hours then check the voltage after charging. Should be 12.6 if all is well. It wasn't. It showed about 11.x when measured at the top/main battery. Took it to dealer, they said both batteries were bad, replaced them both under warranty and life was good (until she traded it weeks later).
Point - the aux battery went bad and eventually took out the main battery to the point it wouldn't hold a charge very long. Dealer said both tested bad.
That fits your description.

2. My JT often doesn't do the ESS thing - I toggle to the ESS page and it says "not ready, battery charging". If it doesn't check the aux battery - how does it know that?
I can drive it for 30+ minutes and it still doesn't work. I've driven it 45 minutes, checked, and it still says "battery charging". Then maybe I'll park for half an hour, come back out and it works.
Then sometimes it won't work, it will say battery charging, then after another 10 minutes of driving, at the next stop - it works. If it doesn't check that aux battery while driving - how does it know the status and suddenly start working? I can get that not read message even if the JT has sat for only 12-18 hours - can't be THAT low. And yet today we drove it for more errands and it worked after only a few minutes/miles, when the truck was warmed up, it worked fine.
It must monitor somehow to know the battery situation as to say not ready battery charging then start working without shutting off and starting again.
Can't be the main battery because the volt meter on the dash says it's running pretty high voltage (these things run higher voltages than anything I've ever owned - if I saw this type of running voltage on my other vehicles I'd say the regulator was shot and over-charging)

The "not ready, battery charging" means the system believes the main battery is not adequately charged for an auto stop based on the IBS reporting. Assuming you already checked the ground cables, try resetting the IBS by unplugging it and see if that helps. Otherwise get the batteries load tested.

 

[ShadowsPapa]

The "not ready, battery charging" means the system believes the main battery is not adequately charged for an auto stop based on the IBS reporting. Assuming you already checked the ground cables, try resetting the IBS by unplugging it and see if that helps. Otherwise get the batteries load tested.

It's more than adequately charged for sure. Will unplug and triple check grounds/connections.
I have noticed that when watching the voltmeter when it's stopped the voltage drops very quickly into the 11 volt range - that's pretty low, IMO - I can let a battery sit on my alternator test stand, run odds and ends with it, test a couple of starters after restoring them, and it still stays up over 12 volts.
It really surprises me to see the voltage drop like that, but I have watched it go down to 11 volts on the dash volt meter display - and it still starts just fine when the light turns green for me.

 

[jebiruph]

It's more than adequately charged for sure. Will unplug and triple check grounds/connections.
I have noticed that when watching the voltmeter when it's stopped the voltage drops very quickly into the 11 volt range - that's pretty low, IMO - I can let a battery sit on my alternator test stand, run odds and ends with it, test a couple of starters after restoring them, and it still stays up over 12 volts.
It really surprises me to see the voltage drop like that, but I have watched it go down to 11 volts on the dash volt meter display - and it still starts just fine when the light turns green for me.

I'm not sure which battery voltage is displayed during an auto stop, the aux battery or the main battery, but they are both powering something and running down during the stop. The battery sensors do fail, so if resetting it doesn't get things working, it may be time to have the dealer check everything.

I expect adding proximity locks has added some additional drain on your batteries. If you aren't driving much, you may want to try an occasional trickle charge, that seems to clear things up for a lot of people.

And your previous mention of really high voltage fits with the system believing the battery needs charged and thus increasing the alternator output to get it charged. My alternator output was 14.5 or higher for years and I wasn't having any issues. When I finally had the dealer check they found a bad main battery. Now my alternator voltage runs lower.

 

[Mr._Bill]

Greatly appreciate the thorough write up! I was just studying up on this, today. I’ll need to read through again to really digest everything.

Had anyone discovered a way to make this a poor man’s Genesis dual battery setup?

The ESS battery is really not big enough for a viable dual battery system. I added a third battery and the same smart Isolator used in the Genesis setup. The Jeep factory setup remains intact, and I have a battery charged by the alternator that the lights and winch are connected to.

 

[ShadowsPapa]

I'm not sure which battery voltage is displayed during an auto stop, the aux battery or the main battery, but they are both powering something and running down during the stop. The battery sensors do fail, so if resetting it doesn't get things working, it may be time to have the dealer check everything.

I expect adding proximity locks has added some additional drain on your batteries. If you aren't driving much, you may want to try an occasional trickle charge, that seems to clear things up for a lot of people.

And your previous mention of really high voltage fits with the system believing the battery needs charged and thus increasing the alternator output to get it charged. My alternator output was 14.5 or higher for years and I wasn't having any issues. When I finally had the dealer check they found a bad main battery. Now my alternator voltage runs lower.

Thanks, helpful info. I'd love to know which it's monitoring as well (volt meter on cluster/dash) as it seems excessive for a normal system - but then these aren't old school battery I suspect.
13.8 to 14.2 is normal for legacy systems - say, like a ZJ or WJ system. Anything more and it's considered over-charging.
Mine has been working lately (as far as ESS) I have not checked the voltage.
It's weird but like once the weather settled to temps 40 or above, it worked better.

 

[jebiruph]

Thanks, helpful info. I'd love to know which it's monitoring as well (volt meter on cluster/dash) as it seems excessive for a normal system - but then these aren't old school battery I suspect.
13.8 to 14.2 is normal for legacy systems - say, like a ZJ or WJ system. Anything more and it's considered over-charging.
Mine has been working lately (as far as ESS) I have not checked the voltage.
It's weird but like once the weather settled to temps 40 or above, it worked better.

When it's running, the batteries and the alternator are all connected together with the higher output of the alternator determining the overall system voltage. When not running the system voltage is the output of both batteries connected in parallel. It's during an auto stop when the batteries are separated that I don't know which battery voltage is displayed.

It's the existence of the IBS reporting the charge and health of the main battery that drives the higher voltages as the system wants to make sure the main battery ready for an auto stop.

 

[jebiruph]

I edited the first post to better explain what happens when the N3 ESS fuse gets blown. I keep reading posts of people getting stranded when this fuse blows, so it's an important concept to understand. Realize that there is no immediate impact when the fuse blows, nothing happens until the aux battery runs down over time, then you're stranded.

Here's the updated last paragraph.
With the high capacity fuse at N3 blown, the aux battery and system electronics are isolated from the alternator and the main battery. The aux battery becomes the only source of power for the system electronics and it is not getting charged from the alternator. Eventually the aux battery will run down and no power will be available to the system electronics, disabling the vehicle. At this point, attempting to jumpstart the main battery won't help because power will still not get to the system electronics.

 

[ShadowsPapa]

Did you ever come up with where the cluster and off-road pages come up with their voltage measurement?
Mine always is running 13.7 to 14.2 or even as high as 14.7 when I look. Today I was watching coordinates and altitudes and other stuff and noticed that my JT was running 12.8 down to 12.6 at times - it was sort of spooky as it was a hot day, we were booking it back home and still a state away from home when I noticed this - I saw your message and thought - oh, crap, hours from home on a nice warm day, we need the AC and a fuse is blown? But it made it hours and miles and later when I checked again it was running 13.8 volts.
Bugs me.
But - obviously that fuse is ok!

 

[j.o.y.ride]

Thread bump reminds me it's time to switch the aux battery back into the circuit for a charge

 

[CivilJeep]

Appreciate the thorough write up! Can you speak to any long term issues you anticipate from disabling the ESS? I installed the Autostop eliminator, and love not having to think about ESS, but I've wondered if it will give me battery problems in the future since its never being used. Thoughts?

 

[Mr._Bill]

Appreciate the thorough write up! Can you speak to any long term issues you anticipate from disabling the ESS? I installed the Autostop eliminator, and love not having to think about ESS, but I've wondered if it will give me battery problems in the future since its never being used. Thoughts?

The Autostop, and similar products, just remembers your choice for activation of ESS events. It does not disable the ESS system. The battery is still being charged.

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