Aux Battery Failure Indications

[Iyamjohng51]

My 2018 Wrangler JL Sport has 30,000 miles. At 7,000 miles, the auxiliary Battery failed and was replaced under warranty. Now, nearly 4 years later, the second auxiliary battery appears to have issues again with some strange symptoms occurring. I am replacing it with a new battery from O'Reilly auto parts as the Mopar batteries are out of stock at the local dealership. Cost of the new battery at O'Reilly is $144 with core charge but it only has a 12-month warranty.

A possible related issue: The blend air door on the A/C & heater distribution housing has been malfunctioning for several months which causes it to try to open & close continuously after the ignition switch is off. That may have drained the aux battery someone suggested. Other indications are random lights and warning messages on the dashboard (e.g. "Air Bag Service" needed). I'm not sure why random messages are generated by failed aux batteries. I hope replacing it cures the problems. BTW: I live in a rural area and very seldom need to use the ESS (Start-Stop) feature as my drives are mostly in locations where it is not triggered.

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[jludave]

I am replacing it with a new battery from O'Reilly auto parts as the Mopar batteries are out of stock at the local dealership. Cost of the new battery at O'Reilly is $144 with core charge but it only has a 12-month warranty.

Why don't you just eliminate the aux battery like most of us have done?

https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/

 

[garykk]

Your main battery is overdue as well.

 

[AndySpill]

My 2018 Wrangler JL Sport has 30,000 miles. At 7,000 miles, the auxiliary Battery failed and was replaced under warranty. Now, nearly 4 years later, the second auxiliary battery appears to have issues again

I know you've already purchased the Aux battery but I might have independently load tested both batteries. Then again at 4 years for this battery, and an undisclosed amount of time that the main battery has been in use, even if the batteries test well, it may be time to swap them. And if you swap one, swapping both is indicated as they are connected in parallel 99.99% of the time, but for an instant at cold crank and during the ESS events you report not running, where a bad battery can bring a good one down.

You can pick up a load tester on the cheap here https://www.harborfreight.com/100-amp-612v-battery-load-tester-61747.html. Simply testing batteries with a multimeter will only give you a reading of their instantaneous voltage, not their ability (the real test) to deliver (and accept back) power. Still more, using either tester properly, multimeter or load, requires in your dual AGM battery JL that you temporarily separate the batteries. Failure to do this can have one battery compensate for the other leading to inaccurate readings.

If you pull all the cables from the main battery's negative terminal and put your tester on that battery' terminals you will get readings for the main battery only. Switch the negative end of your load tester to the temporarily dangling cables (careful for them not to touch metal) and that will give you a reading for the Aux battery only: yes, even as the load tester's positive end remains on the main battery's positive terminal.

Reconnect those cables.

with some strange symptoms occurring. I am replacing it with a new battery from O'Reilly auto parts as the Mopar batteries are out of stock at the local dealership. Cost of the new battery at O'Reilly is $144 with core charge but it only has a 12-month warranty.

A possible related issue: The blend air door on the A/C & heater distribution housing has been malfunctioning for several months which causes it to try to open & close continuously after the ignition switch is off. That may have drained the aux battery someone suggested. Other indications are random lights and warning messages on the dashboard (e.g. "Air Bag Service" needed). I'm not sure why random messages are generated by failed aux batteries. I hope replacing it cures the problems. BTW: I live in a rural area and very seldom need to use the ESS (Start-Stop) feature as my drives are mostly in locations where it is not triggered.

It's possible the issues you describe are battery related. I suspect you'd be less surprised for them to occur if the main battery was experiencing problems, which to my original point it may be. Connect two batteries in parallel as here and a failing battery can bring down a good one.

If you can return the Aux battery and are willing to forgo use of the ESS system we can talk about that as @jludave pointed out prior.

 

[Iyamjohng51]

After replacing both batteries with new ones a few days ago, I got the ESS warning light. I assume I will have to go back to check the connections, unless there is a "reset" process of some sort. I was having issues that appeared to be ESS related but as suggested, I went ahead and replaced both batteries at the same time. The OEM main battery was 5 years old, and the Auxiliary battery was 3 years old. Any ideas why the ESS warning light would come on after doing the work?

 

[AndySpill]

@Iyamjohng51 Hi John:

When you refer to the ESS warning light do you mean to say that you see, near the "E" as in empty letter of the fuel gauge, an icon that shows a capital letter "A," with a near circle around it, followed by an exclamation point: the vehicle's notation that it has turned off the ESS system, or perhaps are you referring to notices in the vehicle's EVIC (dash) that say that ESS isn't ready?

Here's a useful post of reasons that the ESS system might not engage:

https://www.jlwranglerforums.com/forum/threads/start-stop-function.88393/post-1840842

If the problem persists the new batteries, I think, should be load (not multimeter) tested independently, consistent with my prior post in this thread, to make sure that they are capable of holding and delivering charge. Additionally, you may want to make sure that none of the high amp fuses in the Power Distribution Center (PDC), that black box on top, under the hood, near the passenger's front seat, where said fuses reside closest to the driver's side are blown, particularly, I believe, the N3 fuse.

Occasionally, a new battery's a dud.

Picking up a multimeter (not to be confused with a load test meter) to test the fuses, if you don't own one, is not expensive, https://www.harborfreight.com/elect...ters/7-function-digital-multimeter-59434.html and using it to test the fuses via a continuity test, if you are unfamiliar, is done this way:



Another useful thought: https://www.jlwranglerforums.com/fo...not-ready-battery-charging.33802/post-2605865

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