Battery drain out of no reason, and then ESS warning

[tengg2001]

Hi all,

My JLUR is about 5 month old with 5K miles on it, and I'm seeing some strange issue that I couldn't explain. Wondering if anyone can help..
We drove it on Sunday and I parked it in our garage for two days without moving.

On Wednesday, when I was about to go out, first it wouldn't start. Dashboard showing no key fob detected, asking to use key fob to push the start button.

I did. Then I sorts of strange thing started to happen: flashing dashboard, wiper slow move, relay clicking, dome light flashing.
I then checked the main battery voltage by multimeter, it's only 5V..
So I jump started the vehicle and drove out running for one hour. All good except showing message "Auto start/stop unavailable", and the yellow warning sign of ESS is showing up.

Today I went out for a grocery and after I came back, I tried to measure the voltage of the aux battery as well. It turned out:
Main battery voltage 12.58V
Aux battery voltage 10.3V.

Does anyone know if this is normal for the aux battery? Or there's some defect going on causing the main battery keep charging the aux and eventually drain?

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[Some Random Guy]

Something is wrong. It seems to be one of the more prevalent issues with ESS that the aux battery goes bad. A dealer visit should fix it.

 

[OldGuyNewJeep]

Hi all,

My JLUR is about 5 month old with 5K miles on it, and I'm seeing some strange issue that I couldn't explain. Wondering if anyone can help..
We drove it on Sunday and I parked it in our garage for two days without moving.

On Wednesday, when I was about to go out, first it wouldn't start. Dashboard showing no key fob detected, asking to use key fob to push the start button.

I did. Then I sorts of strange thing started to happen: flashing dashboard, wiper slow move, relay clicking, dome light flashing.
I then checked the main battery voltage by multimeter, it's only 5V..
So I jump started the vehicle and drove out running for one hour. All good except showing message "Auto start/stop unavailable", and the yellow warning sign of ESS is showing up.

Today I went out for a grocery and after I came back, I tried to measure the voltage of the aux battery as well. It turned out:
Main battery voltage 12.58V
Aux battery voltage 10.3V.

Does anyone know if this is normal for the aux battery? Or there's some defect going on causing the main battery keep charging the aux and eventually drain?

Yes and yes.

Normal in the sense that the AUX battery sucks and fails early. Also correct that it’s a “defect” if you’re under warranty. Go get it fixed.

Read this: https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/

Buy this: https://www.amazon.com/dp/B07W8KJH44/

 

[Gee-pah]

At least in the 3.6L those batteries are connected in parallel at all times but an instant at crank and during ESS events.

In such situations voltage can flow from the higher voltage battery into the lower voltage battery and, if the lower voltage battery is bad, still not charge it, losing that power to the surroundings.

It's like connecting two water columns of different heights at their bottoms, AND putting a hole in the lower rising water column.

Get a dealer to load test each battery separately. It sounds like your ESS battery, at the very least, is in need of replacement. Anyone who load tests by simply placing the tester's leads on the main battery's terminals, without disconnecting cables will generate a composite load test of both batteries: not something you want.

 

[tengg2001]

Yes and yes.

Normal in the sense that the AUX battery sucks and fails early. Also correct that it’s a “defect” if you’re under warranty. Go get it fixed.

Read this: https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/

Buy this: https://www.amazon.com/dp/B07W8KJH44/

Thank you. The consolidated thread is very very informative.
I'm wondering what the noco genius 5 charger does? Simply charging the battery from home AC and jump start if needed?

 

[OldGuyNewJeep]

Thank you. The consolidated thread is very very informative.
I'm wondering what the noco genius 5 charger does? Simply charging the battery from home AC and jump start if needed?

You should put a battery tender like the Noco (also other good brands out there - whole forum thread about them, somewhere) at least 2x a month. Every other weekend, say.

This is a best practice for all vehicles, but is particularly important on our Jeeps because they have known parasitic draw. Combine that with that fact that it has two batteries, short driving trips just aren’t enough to keep them both charged and healthy.

It’s a wise investment and habit.

https://www.jlwranglerforums.com/forum/threads/best-battery-tender.41317/

https://www.jlwranglerforums.com/forum/threads/battery-tender-for-jl-3-6-with-ess.16736/

https://www.jlwranglerforums.com/forum/threads/looking-to-buy-a-battery-tender.52058/

Eventually you might want to bypass that junky AUX battery like many of us have done (thanks to Jerry’s hard work reverse engineering things): https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/

 

[Gee-pah]

@OldGuyNewJeep's advice about trickle charging makes and sense and I do it. Keeping ESS running is such a strategy's side benefit: prolonging the batteries its primary one.

It won't though address a defective battery incapable of holding or delivering charge: not that he said otherwise.

And while I agree in the value of @Jebiruph Jerry's hard work in helping us build systems that allow us to bypass one or none of our two battery JLs if we choose, such approaches of eliminating one battery from under our hood (invariably the smaller ESS battery) IMHO, should be done, and is only for those who are committed to turning off ESS by factory switch or 3rd party tech. It does though come at the advantage of not allowing our parallel connected ESS battery to become a parasitic drain against the main battery, given that this battery is isolated.

To not turn off ESS in these 1 battery setups is to potentially rob the main battery, designed by Stellantis to be isolated during ESS events (i.e. the main battery) so it has power to crank the engine (in the middle of traffic) of cranking power while it runs accessories in an ESS event. Other vehicles run 1 battery ESS systems, but Wrangler owners are well known for their aftermarket electric drawing appliances---which is probably why the system was designed with 2 batteries. In fairness, the system is designed to crank the engine when voltage drops--but that voltage is suppose to be the voltage of the ESS battery.

IMHO, done correctly, Stellantis should have designed their ESS system with two equally sized batteries that alternate playing the roles of ESS and main battery so as to even their wear. Any battery chemist will tell you the hooking up two dissimilar sized batteries in parallel, as is the case in the 3.6L, is ill advised. But such setups, and the alternator to run them would add to purchase price and subtract from fuel economy: the latter the whole purpose for ESS in the first place.

For the "4 people" that are ESS proponents, without access to shore power for trickle charging but that want ESS to engage, I'm afraid they'll have to move to warmer climates, take longer trips, convert their batteries to two equally sized ones using parts of the (not the entire) Genesis kit*, periodically switch cables to switch which battery is the main one, consider put a solar panel on their "roof rack," and acquire the Trailer-Tow and Heavy-Duty Electrical Group package at purchase, with its larger and more gas guzzling alternator that somewhat defeats the tiny (at the individual owner level that is) gas savings attraction of ESS in the first place.

* the complete Genesis kit is not a solution for ESS saviors. After 6 cranks, the JL will cycle shutting off ESS in such systems when it detects identical voltages in what it thinks are the factory ESS and main batteries. It's a wonderful system for appliance running owners that I by no means wish to bash--just to say that it's by no means the solution to running ESS.

 

[tengg2001]

Thanks everyone for the super helpful tips!

As a follow up, I visited the dealer and they replaced both batteries under warranty.
One thing: the main battery is replaced to a 650 CCA/70AH, while I remember it was 85AH.

Is this expected or it's a mistake?

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