Battery replacement

[BCTrails4x4]

Hey guys, new to Jeep and it’s charging system. Had a failed aux battery that was dead after testing by dealer, replaced it under warranty. Considering it was dead, the whole time the power was being pulled from main, how much voltage life now would main have, and if the aux battery got replaced because it was tested as dead, should the main also be replaced coz of how power was being drained off of that for stuff the aux would have been doing but didn’t?

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[devicemanager]

If you despise ESS, like many of us do, then disconnect the neg aux batt lead (tie off and insulate the end), pull the F42 fuse, and now your main batt will run it all without a parasitic drain when the aux batt fails again. However, this extra load could eventually hang you out to dry. You still need to press the avenger button to disable ESS unless you have a taser or other method to permanently disable it.

 

[Pape]

Starting a hot engine is not that bad on the battery. At 12.7 your battery is mint, especially you did not go like this for long at 1 500 KM on the odo. Maybe you can argue with the dealer about the wear and tear on the main battery and request a replacement, but keep in mind FCA battery are not that great. We usually see a 3 years life from them.

 

[Wbino]

Starting a hot engine is not that bad on the battery. At 12.7 your battery is mint, especially you did not go like this for long at 1 500 KM on the odo. Maybe you can argue with the dealer about the wear and tear on the main battery and request a replacement, but keep in mind FCA battery are not that great. We usually see a 3 years life from them.

I still have my original battery from my April 2021 JL delivery.

 

[Pape]

I still have my original battery from my April 2021 JL delivery.

than you are the exception that confirm the rule

 

[jromanmd]

If you despise ESS, like many of us do, then disconnect the neg aux batt lead (tie off and insulate the end), pull the F42 fuse, and now your main batt will run it all without a parasitic drain when the aux batt fails again. However, this extra load could eventually hang you out to dry. You still need to press the avenger button to disable ESS unless you have a taser or other method to permanently disable it.

@devicemanager So...its been discussed MANY times, but your comment was intriguing. What did you mean hang out to dry? In other words faster battery discharging when isolating the Aux? Iam approaching just over 3 years on my Stock Batteries and am TORN between keeping the OEM setup or by doing what a lot of others have done - disconnecting the Aux, and running on one batt. I have been looking at Bigger Batteries (AGM). Man, I wish I could just make the damn decision already.

 

[Heimkehr]

...if the aux battery got replaced because it was tested as dead, should the main also be replaced coz of how power was being drained off?

The conventional wisdom does suggest replacing both batteries at the same time, not least to establish a matching baseline. It's well-nigh compulsory if you keep the ESS function operational.

If you don't use ESS, then isolating the smaller battery in the accepted method (post 2) is a well-regarded owner mod to consider.

 

[Reinen]

So you can make an informed decision on how to approach this, here's the reason to keep ESS.

First, when using ESS, always replace both Main and Aux at the same time. They are connected in parallel whenever you are not in an active ESS event. Batteries wired in parallel will have a combined lifespan roughly equal to the shortest lifespan of the individual batteries. If you only replace one of the two batteries, the older battery will drastically reduce the lifespan of the new battery. So always replace both at the same time to maximize the lifespan of the pair.

ESS was designed to save a minuscule amount of gas in stop & go conditions. Minuscule enough that nobody cares other than the government. What it is actually useful for is constant passive battery testing. Every time ESS engages you know the batteries have been internally tested and passed testing. If ESS refuses to engage (which inconveniences nobody) you know you have about 2-3 months before you can become stranded with a battery failure. This is more than enough time to inspect, maintain or replace your batteries before you become stranded.

I wheel solo on obscure trails in the SW desert. A place where a battery failure could be life threatening, so I keep ESS active and maintain my batteries as soon as it refuses to engage. I recently had ESS refuse to engage. Turns out that lately I had been doing a lot of short trips with days of sitting idle in between. This is really hard on batteries. Although I had zero symptoms other than ESS, it told me I needed to inspect the batteries. A day on a charger restored my batteries (and ESS) to full functionality. If I did an Aux battery delete I would never have known I was abusing my battery and needed to give it some TLC.

So bottom line is if you never want to be stranded with a dead battery, keep ESS active and use it as a passive warning to perform battery maintenance before you find out about your battery issue the hard way.

 

[comanchepilot]

I still have my original battery from my April 2021 JL delivery.

Not for long.

I had a dual battery set up in my 2013 Rubicon. Optima’s. Date code July 2015. Consider that for a moment.

 

[Wbino]

Not for long.

I had a dual battery set up in my 2013 Rubicon. Optima’s. Date code July 2015. Consider that for a moment.

Yeah the plan is to replace it before the real winter months arrive.
I think having Etorque has contributed to the longevity of the 12v battery.

 

[Reinen]

Yeah the plan is to replace it before the real winter months arrive.
I think having Etorque has contributed to the longevity of the 12v battery.

It's primarily driving habits. Sitting idle is really hard on batteries in a JL. If you drive it daily and drive long enough to fully recharge the battery it will maximize its lifespan.

 

[BCTrails4x4]

Starting a hot engine is not that bad on the battery. At 12.7 your battery is mint, especially you did not go like this for long at 1 500 KM on the odo. Maybe you can argue with the dealer about the wear and tear on the main battery and request a replacement, but keep in mind FCA battery are not that great. We usually see a 3 years life from them.

This is actually cold engine, I just got off work and was warming up my Jeep not even 2 min. Jeep is new(2025) but the engine light and “Avengers” symbol was lit up when I purchased coz initially it was sitting in their show room(13kms on the dash). They had a tech just reset the code so they disappeared, but that’s when my OCD said that’s not fixing the problem, that’s when I had forced the issue for them to test the battery. My OCD lit up again when I noticed the cover panel in front of the gear shift was open(where the pull lever is to disengage gear so you can put in “N” to be able to tow or move Jeep if it’s stuck), is this some reason to be opened if there’s battery issue?
Also my previous Jeep(2024)was holding 14.0 even up to 2yrs. of owning it.

 

[Heimkehr]

the engine light and “Avengers” symbol was lit up

"Avengers" symbol?

 

[Pape]

This is actually cold engine, I just got off work and was warming up my Jeep not even 2 min. Jeep is new(2025) but the engine light and “Avengers” symbol was lit up when I purchased coz initially it was sitting in their show room(13kms on the dash). They had a tech just reset the code so they disappeared, but that’s when my OCD said that’s not fixing the problem, that’s when I had forced the issue for them to test the battery. My OCD lit up again when I noticed the cover panel in front of the gear shift was open(where the pull lever is to disengage gear so you can put in “N” to be able to tow or move Jeep if it’s stuck), is this some reason to be opened if there’s battery issue?
Also my previous Jeep(2024)was holding 14.0 even up to 2yrs. of owning it.

14.0 is actually the alternator supplying voltage to charge the battery. the battery itself is 12v.
When cruising you should see 13~14.7. I suspect the 12.7 was during a stop where the engine was shut off.

 

[Ridge2Far]

"Avengers" symbol?

ESS Warning <——> Marvel Comics Avengers Logo

I have enough trouble remembering acronyms like ESS (or is it ASS?), IBS (or is it EBS?), PCR and PDC.

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