Dual AGM Battery JL Question

[AndySpill]

Does anyone have confirmation regarding whether, at the end of an engine start stop (ESS) event, the two batteries are reconnected in parallel before or after the (successful) engine crank?

TIA.

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[YBABRAT]

Batteries will reconnect after engine starts. Aux is only used when stop start feature is active and engine cranks. Charging depends on both batteries having equal or near equal SOH. Problem is if main battery has been depleted... not enough charge from multiple stops within a 30 minute interval, the single stage charging will over charge the Aux battery. It's a nice idea but too problematic with gremlins when batteries don't have enough charge during startup.

 

[Reinen]

Does anyone have confirmation regarding whether, at the end of an engine start stop (ESS) event, the two batteries are reconnected in parallel before or after the (successful) engine crank?

TIA.

They are reconnected after the engine crank. The whole point of it is to ensure electronics have clean steady power to manage the restart and aren't browned out by the starter's heavy power draw.

 

[AndySpill]

I ask because both batteries are separated on dual AGM battery JLs for an instant at cold crank to test the Aux battery and then brought together again prior to the cold crank.

I know this because you can cold crank and dual AGM battery JL with just a charged Aux battery.

@YBABRAT , @Reinen : how do you guys know what you claim is the case. Of course I'm not saying your lying or wrong...I believe you..it's just that in the case of the cold crank there's proof that the behavior is opposite of that described.

Maybe if I feel adventurous I'll put a cabin area operated relay on the main battery to disconnect it from the vehicle, during an ESS event (beyond that done by the vehicle during this event, that is) in my residential area, and see what happens.

 

[azjl#3]

Batteries will reconnect after engine starts. Aux is only used when stop start feature is active and engine cranks. Charging depends on both batteries having equal or near equal SOH. Problem is if main battery has been depleted... not enough charge from multiple stops within a 30 minute interval, the single stage charging will over charge the Aux battery. It's a nice idea but too problematic with gremlins when batteries don't have enough charge during startup.

since you seem like the man in the know... I want to keep it simple when time comes to replace/remove the aux battery. My idea to bypass the aux problem, remove battery, run jumpers of about 10ga wire back to the big battery, with a 30a breaker. Walla, jeep thinks it has an aux, allows jeep to "bypass" the aux/main when its doing its ESS buffoonery. No aux needed, and when time comes, I can install the next size up main battery by removing stupid plastic spacer block in battery tray.

 

[YBABRAT]

since you seem like the man in the know... I want to keep it simple when time comes to replace/remove the aux battery. My idea to bypass the aux problem, remove battery, run jumpers of about 10ga wire back to the big battery, with a 30a breaker. Walla, jeep thinks it has an aux, allows jeep to "bypass" the aux/main when its doing its ESS buffoonery. No aux needed, and when time comes, I can install the next size up main battery by removing stupid plastic spacer block in battery tray.

If you remove AUX battery, you might as well try and remove its pcr and cables from the main battery terminals. It's a bit time consuming in doing so, but it will allow for the use of the existing unused cables. Move the power from Aux to main battery and you'll have an extra ground and power cable from aux box. No need to add fuses, just remove N3 cable at the fuse box junction. N1 has the power cable that you will move to main battery power. You must have a H7 or better battery.

Lowe has like oem cloth tape around $5.00 dollars in the electrical section. Works well and keeps an oem look with wrapping wires.

I don't know why some want to use a fuse on the fuse box. It basically protects its self with all the needed fuses. I got into a cyclical convo with another member, and gave up to keep any further argument at bay. If you followed current path, the fuse would point right back at the power coming in, never seeing amperage draw, unless a floating ground is achieved. That is another issue that can happen with a dual alternator and bad ground or with generator motor and bad ground. Old style alternators had blown diode assembly would act as a motor when engine was off, literally draining the battery in minutes.

 

[Reinen]

I ask because both batteries are separated on dual AGM battery JLs for an instant at cold crank to test the Aux battery and then brought together again prior to the cold crank.

I know this because you can cold crank and dual AGM battery JL with just a charged Aux battery.

@YBABRAT , @Reinen : how do you guys know what you claim is the case. Of course I'm not saying your lying or wrong...I believe you..it's just that in the case of the cold crank there's proof that the behavior is opposite of that described.

Maybe if I feel adventurous I'll put a cabin area operated relay on the main battery to disconnect it from the vehicle, during an ESS event (beyond that done by the vehicle during this event, that is) in my residential area, and see what happens.

On cold cranks the batteries are linked for maximum power to the starter. The electronics can reset at that point if they get browned out because the Jeep must be in Park with brake depressed to cold start. It's not in full operation just yet as it would be during a warm start.

What I said was only in reference to warm ESS starts. If the Main is somehow disconnected for the warm start, ESS won't engage. I'm not sure what will happen if the Main is disconnected after an ESS shutdown is initiated, but when is that ever going to happen?

 

[AndySpill]

On cold cranks the batteries are linked for maximum power to the starter. The electronics can reset at that point if they get browned out because the Jeep must be in Park with brake depressed to cold start. It's not in full operation just yet as it would be during a warm start.

What I said was only in reference to warm ESS starts. If the Main is somehow disconnected for the warm start, ESS won't engage. I'm not sure what will happen if the Main is disconnected after an ESS shutdown is initiated, but when is that ever going to happen?

Thanks.

I completely get that your comments were specific to warm, post ESS engine cranks, not cold cranks.

Still more, it makes perfect sense to me that the wise approach, as you describe, is for post ESS engine cranks to happen against the ESS event preserved main battery only, not a combined main and Aux battery combo: which if it were the case of course would find the main battery taxed not only to power the engine starter, but deal, prior to the post ESS engine crank, with the voltage differential of a somewhat depleted Aux battery first being connected to it.

But how do you know this the case? (Sorry to be pesty.)

For example, here's how I know that for cold cranks, both batteries effect the engine start, as a disconnected main battery with an energized Aux is enough to turn over the engine.

Many thanks.

(P.S. failure to start with a disconnected or depleted Aux battery, as this older video shows, was addressed with TSB 18-092-19, and from the factory on all dual AGM JL models starting with the latter part of the model year 2018 lineup, and model years thereafter.)

 

[AndySpill]

since you seem like the man in the know... I want to keep it simple when time comes to replace/remove the aux battery. My idea to bypass the aux problem, remove battery, run jumpers of about 10ga wire back to the big battery, with a 30a breaker. Walla, jeep thinks it has an aux, allows jeep to "bypass" the aux/main when its doing its ESS buffoonery. No aux needed, and when time comes, I can install the next size up main battery by removing stupid plastic spacer block in battery tray.

Hi Scott:

You seem to have two goals, not conflicting. The first being the (optional) physical removal of the Aux battery (many people, as you probably know just disconnected the cable that leads from its negative terminal to the main battery's negative terminal....at the main battery's negative terminal, and then insulate the loose end) and the second goal is tokeep things simple.

From where I'm standing I'd be inclined, rather than to reroute the cables that lead to and from the Aux battery you are yanking, is to yank those cables as well and pull Fuse 42, the latter, in so doing, preventing, without any fuss in the way of vehicle warning lights, energization of the Power Control Relay (PCR), in so doing preventing the vehicle from isolating the Aux battery cables to be the only thing powering the vehicle for an instant prior to cold crank (to test the Aux battery) and during the ESS events you want no part of.

Pulling Fuse 42 means calls for power go to all batteries, all the time, of which, since you'll only have the main battery connected, means calls for power always go only to the main battery.

If something "rubs you wrong" about pulling Fuses then yes, reroute those Aux battery cables, or proceed as above, but fused jumper N1 to N2.

https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

There's yet a 3rd way. Disconnect and optionally remove the Aux battery and its cables and stop there.

Attempt to crank. Expect it to fail. Try again. This time (since you're not running an early model 2018 without TSB 18-092-19) the vehicle should attempt the crank off the main battery and if successful, throw an ESS off idiot light in the dash, effectively turning off ESS for you without a button push or tech--that is if you don't mind idiot lights.

The downside to this approach is that people on the board believe this idiot light is a sign, under normal operation, of a potential problem--a "canary in the mine" if you will, and that its constant illumination can potentially mask problems.

 

[Reinen]

But how do you know this the case? (Sorry to be pesty.)

I have read this in an official Mopar document but I don't have the time to find it and link it. I'm subtly trying to get out of doing that.

But I assure you I looked for this info myself, found it, and that's what it said. I just don't have the link handy.

 

[azjl#3]

Hi Scott:

You seem to have two goals, not conflicting. The first being the (optional) physical removal of the Aux battery (many people, as you probably know just disconnected the cable that leads from its negative terminal to the main battery's negative terminal....at the main battery's negative terminal, and then insulate the loose end) and the second goal is tokeep things simple.

From where I'm standing I'd be inclined, rather than to reroute the cables that lead to and from the Aux battery you are yanking, is to yank those cables as well and pull Fuse 42, the latter, in so doing, preventing, without any fuss in the way of vehicle warning lights, energization of the Power Control Relay (PCR), in so doing preventing the vehicle from isolating the Aux battery cables to be the only thing powering the vehicle for an instant prior to cold crank (to test the Aux battery) and during the ESS events you want no part of.

Pulling Fuse 42 means calls for power go to all batteries, all the time, of which, since you'll only have the main battery connected, means calls for power always go only to the main battery.

If something "rubs you wrong" about pulling Fuses then yes, reroute those Aux battery cables, or proceed as above, but fused jumper N1 to N2.

https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

There's yet a 3rd way. Disconnect and optionally remove the Aux battery and its cables and stop there.

Attempt to crank. Expect it to fail. Try again. This time (since you're not running an early model 2018 without TSB 18-092-19) the vehicle should attempt the crank off the main battery and if successful, throw an ESS off idiot light in the dash, effectively turning off ESS for you without a button push or tech--that is if you don't mind idiot lights.

The downside to this approach is that people on the board believe this idiot light is a sign, under normal operation, of a potential problem--a "canary in the mine" if you will, and that its constant illumination can potentially mask problems.

great info thanks

 

[Compression-Ignition]

No dog in the fight, but it seems like you are missing an option.



Remove the aux. battery completely from the system.

Reroute aux. cables to the remaining battery's terminals. May need to drill them out to a larger size or other simple modification for attachment purposes.

Use your E.S.S. removal device to keep any and all E.S.S. events from ever occurring again with one single press of a button. I prefer this one. SMART STOPSTART

Done

 

[AndySpill]

No dog in the fight, but it seems like you are missing an option.



Remove the aux. battery completely from the system.

Reroute aux. cables to the remaining battery's terminals. May need to drill them out to a larger size or other simple modification for attachment purposes.

Use your E.S.S. removal device to keep any and all E.S.S. events from ever occurring again with one single press of a button. I prefer this one. SMART STOPSTART

Done

Hi Roy:

The need to reroute those cables you mention is a product of the fact that the vehicle isolates the Aux battery for an instant at cold crank (and during ESS events), and in the absence of that battery (or it connected but lacking ample power) will prevent a JL from cold cranking in different ways.

In early model 2018 JLs (all dual AGM battery vehicles) the absence of a(n) energized Aux battery would leave you stranded. In later model dual AGM battery JLs (not all recent model year JLs are dual AGM battery vehicles) or those earlier ones flashed with TSB 18-092-19, the initial cold crank will not work, but subsequent ones are attempted against just the main battery and if successful, future cold cranks should occur on the first try, all as the vehicle lights up the ESS off light in the dash.

As I mentioned in this thread, some might consider this light a feature: the vehicle turning ESS off for you if you don't mind idiot lights--but it is advised against as that ESS off light 's illumination under normal circumstances, it is reasoned, can disclose possible problems that its continual illumination under this approach can mask.

But...all this said, and again to reiterate, this need to reroute the cables you describe is rendered obsolete if the vehicle is prevented from isolating the Aux battery (cables), which happens when you pull Fuse 42, and prevent the Power Control Relay (PCR) from being energized---a silent operation--in so doing allowing all connected batteries to power all vehicle electrical demands..which boils down to just the main battery providing said power given the Aux battery's removal.

The PCR is a normally closed relay. Its energization, which can't happen if Fuse 42 is pulled, is what separates the batteries, as happens not only for the instant described prior to cold crank for testing, but during the ESS events you propose to prevent from engaging.

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