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Auxiliary Battery - where is it and what's its function?

Zman1403

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I am new to the Jeep world. Took possession of my 2020 Ribicon yesterday. Only 2,696 miles. It is the eco diesel model. I have seen numerous You Tube videos showing how to change the Auxiliary battery. I don’t need to do that now. However I cannot find even a mention of it in the owners manual or the eco diesel supplement. Can anyone advise where it is and what exactly it’s function is. I am planning to purchase a secondary power source like the Goal Zero to power my Alpicool refrigerator. However I still want to know about the auxiliary battery.
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brewdad

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It is a small motorcycle size battery located beneath the main battery.
 

Heimkehr

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I am new to the Jeep world. Took possession of my 2020 Ribicon yesterday. Only 2,696 miles. It is the eco diesel model. I have seen numerous You Tube videos showing how to change the Auxiliary battery. I don’t need to do that now.

I still want to know about the auxiliary battery.
On my 2021 non-eTorque 2.0T, the auxiliary battery restarts the engine when the Engine Start Stop function is turned on.
 

MEHillwalker80

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On my 2021 non-eTorque 2.0T, the auxiliary battery restarts the engine when the Engine Start Stop function is turned on.
You have it backwards. The Aux battery keeps keeps accessories and computer alive when the ESS stops the engine. The size of the Aux battery is insufficient to provide cranking current to the starter motor anyway. It only is there to keep systems alive when the alternator is not producing anything. Consider what happens to the systems when the Aux battery fails to keep the main computer happy. Lots of lights and warnings.

One of the best writeups on this is here: https://www.jeepfan.com/tech/how-electronic-start-stop-ess-works-on-the-jeep-wrangler-jl/
 

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Rhinebeck01

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You have it backwards. The Aux battery keeps keeps accessories and computer alive when the ESS stops the engine. The size of the Aux battery is insufficient to provide cranking current to the starter motor anyway. It only is there to keep systems alive when the alternator is not producing anything. Consider what happens to the systems when the Aux battery fails to keep the main computer happy. Lots of lights and warnings.

One of the best writeups on this is here: https://www.jeepfan.com/tech/how-electronic-start-stop-ess-works-on-the-jeep-wrangler-jl/
@MEHillwalker80

Actually that write-up that you linked to has lots of misinformation in it.... Suggest you research here on the forum for spot on info in regard to the dual battery system in the JL/JT.

By the way, the Aux/ESS battery has no problem at all starting the JL when the Main is depleted...
 

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You have it backwards. The Aux battery keeps keeps accessories and computer alive when the ESS stops the engine. The size of the Aux battery is insufficient to provide cranking current to the starter motor anyway. It only is there to keep systems alive when the alternator is not producing anything. Consider what happens to the systems when the Aux battery fails to keep the main computer happy. Lots of lights and warnings.

One of the best writeups on this is here: https://www.jeepfan.com/tech/how-electronic-start-stop-ess-works-on-the-jeep-wrangler-jl/
The linked article was written when the JL generation was new. Possibly, the author wasn't yet in possession of all the facts. The article mentions only the 3.6 Pentastar, not the 2.0T engine, and makes no mention at all of an auxiliary battery or the function(s) it serves.

The foregoing is for me just an academic discussion, anyway. I've disabled the ESS function with a proprietary harness.
 

Rhinebeck01

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The linked article was written when the JL generation was new. Possibly, the author wasn't yet in possession of all the facts. The article mentions only the 3.6 Pentastar, not the 2.0T engine, and makes no mention at all of an auxiliary battery or the function(s) it serves.

The foregoing is for me just an academic discussion, anyway. I've disabled the ESS function with a proprietary harness.
@Heimkehr

You have not "disabled the ESS function"...

All that harness you bought does, is in essence, push the ESS button for you and no more. It basically remember's whether ESS was on or off when the JL was last used and has it doing the same same for you again, automatically.
 

Gee-pah

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Can anyone advise where it is
Is the battery actually below the main battery on the OPs diesel? From what I understand, the main battery and Power Distribution Center (PDC): the intelligent fuse box switch places in the diesel JL as opposed to say the 3.6L JL.

I mean it would make sense if the Aux battery stays in the same place on the Eco Diesel model, and just the main battery and PDC switch places.

and what exactly it’s function is.
There's literal and interpretive answers to that question. The literal one is to keep your appliances running while the engine is turned off at a braked stop of some duration beyond a stop sign (e.g. traffic light) during an ESS evenet to spare the main battery so it can effect the ** bulk of the crank of the engine when the ESS event is terminated. At least that's how it works in the 3.6L.

** both batteries energize the crank, again, at least in a 3.6L engine.

A more interpretive answer is to improve reported fuel economy of the Jeep fleet so as to avoid EPA penalty, whose cost would have to be shared with the consumer.

Another interpretive answer is a poorly designed system that recognized the need to spare the cranking battery from the draw of all the potential appliances Wrangler owners run, that would have been better designed by making not only both batteries of the same size, but alternating which one was the cranking, and which one was the Aux battery every few engine cranks IMHO. Battery purists talk about the disadvantages of hooking to dissimilar sized batteries up in parallel, as is the case here. A single battery ESS would probably be okay for a minivan (as some are designed) but not a modded Wrangler with energy hungry (lights, etc.) gear.

I am planning to purchase a secondary power source like the Goal Zero to power my Alpicool refrigerator. However I still want to know about the auxiliary battery.
There have been some excellent writeups here, I don't know if they apply to the Eco diesel as much as they do the 3.6L model, that allow the two batteries to run as factory, or allow the JL to run on just one of them, or both batteries constantly in parallel, even in ESS events when the batteries are suppose to be isolated.

Such functionality can allow appliances at the campsite to run off just one of the batteries, why the other is preserved for cranking the rig, where after the depleted battery can be rejoined to the alternator post crank to recharge.

Despite this I'd recommend a dedicated battery to run appliances like a refrigerator. But then discussion turns to how and when this dedicated battery is recharged, from shore power, to solar (like your Goal Zero can,) to alternator/starter battery only when the engine is cranked, etc.
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