Secondary Battery

[Zandcwhite]

Yes, Aux is AGM Lead Acid.

Flooded carb? That has nothing to do with a JL. A completely different and irrelevant scenario where you keep engaging the starter without starting the engine to recharge the battery. That is night & day different from normal ESS use.

ESS a smart system. If you do hit a lot of lights in rapid succession ESS will stop engaging if the battery needs to recharge. If the batteries are failing it won't engage. It's also a smart recharging system which will pump up or reduce the charging voltage as necessary, which also didn't exist in the carb days. ESS will never run the battery dead in a JL. It will stop engaging well before that happens.

What can't be controlled is how long the JL sits parked with electronics parasitic draw, which drains and sulfates the batteries. When that happens, over time a significant voltage drop can occur when the starter engages for a cold start. That is what Aux is there to avoid. On the JL, insufficiently powered electronics means complete engine failure. The engine is no longer physically controlled by driver actions anymore.

Well you've almost come full circle, the aux battery is there for the voltage drop from starts...but not the ess ones?

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[Jebiruph]

I don't see it that way because engine starts aren't particularly hard on AGM/Lead-Acid batteries. It's always a large sudden discharge followed by an immediate recharge. That's the AGM/Lead-Acid wheelhouse, it's the best kind of battery for those functions.

What is also new are OEM proximity keys, remote start, OTA updates, security, etc. All always-on functions. They don't require much power but they drain the batteries slightly with a long time until recharge. That's the AGM/Lead-Acid battery's Achilles Heel. It's the worst kind of battery for those functions, it slowly and progressively damages the battery.

That's the primary reason for Aux, not ESS. This is exemplified by how an alternate battery is used for electronic functions whenever possible (i.e. eTorque & 4XE). An AGM Aux is literally a last resort.

There is no correlation between the use of the alternate battery and the existence of advanced electronics with Jeeps, a Jeep can have advanced electronics and no alternate battery. But no Jeep uses an alternate battery that doesn't have Stop/Start.

Etorque powers the electronics and the 12v starter off of a single 12v battery, the alternate 48v battery does not power the 12v electronics. The 392 has advanced electronics but doesn't have ESS or an aux battery, based on your argument shouldn't it have an aux battery? My wife's Cherokee has advanced electronics and no aux battery.

With the JL/JT, both batteries power everything except during an ESS event, so both batteries power the electronics when the engine is powered off and will be degraded in parallel, not just the aux. And many have run with the aux battery disconnected for years with no adverse affect on the electronics.

When the new Cherokee's first came out with a single battery ESS system, people were getting stranded in intersections when the batteries failed an ESS restart after powering the electronics during auto stop. The aux battery system was designed provide auto stop power to the electronics while holding the main battery power in reserve for the restart.

 

[Reinen]

When the new Cherokee's first came out with a single battery ESS system, people were getting stranded in intersections when the batteries failed an ESS restart after powering the electronics during auto stop. The aux battery system was designed provide auto stop power to the electronics while holding the main battery power in reserve for the restart.

That's exactly my point. If a failing single battery can fail an ESS restart, it can fail a cold start as well. It's just the luck of the draw on which start just squeaks by and which start fails. Either way, the engine start failed because the battery couldn't provide adequate power to the electronics while simultaneously powering the starter. That problem exists regardless of whether ESS exists.

Since an ESS start failure is usually followed by a lot of public drama, then yes, the forced introduction of ESS certainly made designers care more about addressing the already existing problem. ESS didn't cause the problem, it just changed the ramifications of the existing problem from a private "in your driveway" problem to a public "in the intersection" problem.

That does not mean the functionality of Aux has anything to do with ESS. It's function is an electronics and communications battery, isolated from the Main battery during starter engagement, that ensures the electronics have stable power during start events. This benefits you whether you leave ESS enabled or disabled. Everyone uses the starter motor to start the engine.

 

[Zandcwhite]

That's exactly my point. If a failing single battery can fail an ESS restart, it can fail a cold start as well. It's just the luck of the draw on which start just squeaks by and which start fails. Either way, the engine start failed because the battery couldn't provide adequate power to the electronics while simultaneously powering the starter. That problem exists regardless of whether ESS exists.

Since an ESS start failure is usually followed by a lot of public drama, then yes, the forced introduction of ESS certainly made designers care more about addressing the already existing problem. ESS didn't cause the problem, it just changed the ramifications of the existing problem from a private "in your driveway" problem to a public "in the intersection" problem.

That does not mean the functionality of Aux has anything to do with ESS. It's function is an electronics and communications battery, isolated from the Main battery during starter engagement, that ensures the electronics have stable power during start events. This benefits you whether you leave ESS enabled or disabled. Everyone uses the starter motor to start the engine.

Can we get one example of a vehicle with an AUX battery that doesn't have ESS? If they are unrelated and it is just about a cold start then surely it exists?

 

[Jebiruph]

That's exactly my point. If a failing single battery can fail an ESS restart, it can fail a cold start as well. It's just the luck of the draw on which start just squeaks by and which start fails. Either way, the engine start failed because the battery couldn't provide adequate power to the electronics while simultaneously powering the starter. That problem exists regardless of whether ESS exists.

Since an ESS start failure is usually followed by a lot of public drama, then yes, the forced introduction of ESS certainly made designers care more about addressing the already existing problem. ESS didn't cause the problem, it just changed the ramifications of the existing problem from a private "in your driveway" problem to a public "in the intersection" problem.

That does not mean the functionality of Aux has anything to do with ESS. It's function is an electronics and communications battery, isolated from the Main battery during starter engagement, that ensures the electronics have stable power during start events. This benefits you whether you leave ESS enabled or disabled. Everyone uses the starter motor to start the engine.

Then why is it only isolated during an auto stop restart and not during a cold start?

The aux battery doesn't exist to protect the power to the electronics, it exists to protect the power to the starter.

 

[Reinen]

Then why is it only isolated during an auto stop restart and not during a cold start?

The aux battery doesn't exist to protect the power to the electronics, it exists to protect the power to the starter.

It's isolated on cold starts as well. This is why 2018 JLs were very difficult to jump start. You'd jump Main, try to start, the batteries would isolate (also isolating Aux from the jump start) and Aux couldn't power the electronics, even though Main had all the power it needed from the jump.

This was resolved with an update. Now, if the first press of the Start button fails a voltage test a 2nd press will attempt to start without isolating Main & Aux, where both get the benefit of the jump.

The starter doesn't need protection. If it doesn't get full power it just turns slower which can still be enough to start the engine. Not a big problem. If the electronics don't get enough power, which can easily happen during the starters heavy draw, the ecu can't communicate the engine and manage the start. And there will be zero chance of starting the engine no matter how fast the starter is cranking it over.

 

[Jebiruph]

It's isolated on cold starts as well. This is why 2018 JLs were very difficult to jump start. You'd jump Main, try to start, the batteries would isolate (also isolating Aux from the jump start) and Aux couldn't power the electronics, even though Main had all the power it needed from the jump.

This was resolved with an update. Now, if the first press of the Start button fails a voltage test a 2nd press will attempt to start without isolating Main & Aux, where both get the benefit of the jump.

The starter doesn't need protection. If it doesn't get full power it just turns slower which can still be enough to start the engine. Not a big problem. If the electronics don't get enough power, which can easily happen during the starters heavy draw, the ecu can't communicate the engine and manage the start. And there will be zero chance of starting the engine no matter how fast the starter is cranking it over.

You're still mostly wrong. The system briefly isolates the aux battery during a cold start for testing, then it's reconnected with the main battery for the actual start.

Test it yourself, go out and disconnect your main battery, leave the aux battery connected and start the engine. It will start the first time every time because the aux battery is fully connected to everything during a cold start.

Now connect the main battery, disconnect the aux battery and start the engine. The dash lights will go blank as the disconnected aux fails it's test and the engine won't crank. The ESS error light gets turned on and ESS is disabled. Until the ESS error gets cleared, there will be no further cold start testing of the aux battery and ESS will remain disabled because the purpose of the aux battery is to facilitate ESS.

The problem with the 2018 was when the aux battery failed the test, ESS never got disabled and the aux battery would get retested and fail over and over again. The update was to disable ESS and further testing after the initial failure because the purpose of the aux battery is to facilitate ESS.

Here's what it looked like in 2018.

 

[Borg]

I have a JLU with eTorque. I’m doing some reading on the ecoboost and eTorque system to better understand them so I can troubleshoot should a problem arise.

One problem has arisen thus far, I had a dual dash cam system with its own battery that charged off the 12v lead-acid. With that setup and my driving style being mostly short, city trips, the stop/start feature stopped working entirely. It would say “Stop/start not ready battery charging”.

To remedy that, I hooked up a 2A battery charger overnight. By the second or third day, I have Stop/start all the time and the battery reads 14V up from something like 13.4v.

My assumption is the camera (though it’s not supposed to) was drawing too much from the 12v while the Jeep isn’t running. The 48v has to recharge that battery. Because of the draw and my driving, the 48v couldn’t maintain a charge high enough to support stop/start.

Can anyone sanity check my thinking here? Thank you for the info.

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