Aux battery issue, need second opinion

[WhitneyWillys]

Having read several highly informative posts about AUX battery issues on this forum, I strongly suspect I too am victim of the same. I thought I will share my symptoms and seek second opinion.

Do you concur, the following behavior most likely indicates a failing Aux battery?

1. 2021 JLU Willy's, 2.0 with ESS, 32K miles, just out of warranty (sigh).
2. ESS has not worked for a while already.
3. AUX switches not available warning has been coming up lately, they do become available after about 30s of driving.
4. Per the dashboard screens, the primary batter maintains 12.4-12.6v in Acc mode and 14v+ in full ignition.
5. As such had no issues till this past weekend when I went offroad/camping.
6. At camp, the Jeep was not turned on (ignition) for about 48 hours. It was very cold. Doors were opened closed several times for normal camp style use. I even slept in it. When I tried starting the Jeep after those 48 hours, it wouldn't start. I had to jump it. It started fine after that.
7. But now, everytimeI start it, I have the Jeep warning me about ESS needing service, in addition to the AUX switches not being available.
8. On occassion, when I have the Jeep engine running, and the doors are opened to let someone out, I get key fob has left the Jeep warning. This has happened a couple.of times.
9. The main battery still looks fine from the dashboard screens.

Is my Aux battery failing? Could it have been responsible for draining my main battery?

Thanks.

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[bonniejf]

others will surely chime in... but your batteries are 3 yrs old at least. Don't just replace the aux battery, replace both, now. There's a ton of info already posted on this forum that explains how and what.

 

[Stetson]

others will surely chime in... but your batteries are 3 yrs old at least. Don't just replace the aux battery, replace both, now. There's a ton of info already posted on this forum that explains how and what.

Agee 100%. Similar symptoms in my ‘19 and I replaced both. All ‘strange issues’ disappeared.

replace both barriers and you don’t have to worry about it for another couple of years

Stetson

 

[rohdawg]

Is my Aux battery failing? Could it have been responsible for draining my main battery?

Yes.
Yes.

Replace both of them or bypass the aux and replace the main and never have the problem again.

 

[DigDug69]

I have a 23 Willy's this is a common issue with the auxiliary battery. It is bad. The auxiliary battery is still pulling power from your main battery which in return caused it to fail on you.
It was suggested to me, from off-road techs to disconnect auxiliary battery from main battery and disable the start/stop function (don't really save any fuel). Or replace w the Genesis dual battery system made for Jeeps

 

[AndySpill]

@WhitneyWillys Sam: Your symptoms and battery age suggest ESS battery failure, but whether this battery needs replacement is definitively made by hooking it up to a load tester; not to be confused with a volt meter as follows:

Two black cables from the factory end at the main battery's negative terminal. One of those cables has as its other end the body ground on the passenger's side under the hood. Leave that cable untouched. But temporarily disconnect the other cable and hook it to the negative side of a load tester.

The positive side of the load tester can go on the main battery's positive terminal. This will test the ESS battery.

Reattach that cable after the load test.

An even more fundamental question is if you want to run with the ESS battery at all. If you're willing to do without the ESS system engaging it's pretty easy to bypass the ESS battery. Four steps are required, the first you did when disconnected the cable. The second step it to wrap the cable end in electric tape, the third step is to pull Fuse 42 from the Power Distribution Box, and the fourth is to turn ESS at the dash by pressing the ESS off button or buying product to turn ESS off for you.

You may still need a new main battery. Load test that by--with that cable still detached, moving the negative lead of the load tester over to the main battery's negative terminal.

Oh--that dash screen showing battery voltage you mention, with the factory wiring that's the voltage of both batteries unless you're in an ESS event, in which case it's only the ESS battery.

 

[WhitneyWillys]

@AndySpill thanks for the detailed response. Couple of questions.

I am quite willing to run without the Aux battery. Is it safe to say that ESS is the only function I lose if I delete the Aux battery from the circuit and follow your other instructions? Things like the Aux switches etc., do they remain instantly available?

I don't have a load tester unfortunately. While a volt meter is not a substitute, what numbers should I expect from the Aux to deem it as failing? Just curious. This I can check.

I suppose I can save myself the hassle of going to the dealership, just try your suggested steps, run a few days without the Aux, and see how it goes, right? I will swap out the main battery in the short term myswlf. At least I will be saving myself the hassle of dealing with the fender liner etc to reach the Aux!

 

[The Last Cowboy]

The aux battery just keeps power to the system while the ESS is in stop mode, the main battery powers the starter. As I understand it, when the aux battery dies, all power is drawn off the main while the dying ESS battery is also pulling current from the main.

Elimination of the aux battery is the best thing you can do. Replace the main with an H7/94R and you will likely be okay with ESS functioning, but only if the aux is taken out of the system.

ESS will function with the aux battery gone, you will need to need to disable it if you don't want it to function anymore.

 

[TheNewGuy]

@WhitneyWillys

Oh--that dash screen showing battery voltage you mention, with the factory wiring that's the voltage of both batteries unless you're in an ESS event, in which case it's only the ESS battery.

It's my understanding that the voltage reading displayed on the dash is not the battery voltage but the voltage output of the alternator. A low reading (12.5-13.5) means your batteries are more or less fully charged, the higher the reading (14.0+) means it's working to charge the batteries
Someone can correct me if I'm wrong.

 

[AndySpill]

It's my understanding that the voltage reading displayed on the dash is not the battery voltage but the voltage output of the alternator. A low reading (12.5-13.5) means your batteries are more or less fully charged, the higher the reading (14.0+) means it's working to charge the batteries
Someone can correct me if I'm wrong.

This may be true. It is though the ESS battery voltage in an ESS event though.

 

[WhitneyWillys]

The aux battery just keeps power to the system while the ESS is in stop mode, the main battery powers the starter.

I don't fully understand this. Let's say the Aux battery is connected as intended and the Jeep is in the ESS stop mode. In this state, do all electronics systems, such as radio etc., get powered by the Aux battery? At the end of the ESS stop, when the break is released, does the Aux battery get used to power up the engine again?

I am asking so as to understand what additional load I will be putting on the main battery if I delete the Aux. Especially if I keep using the ESS feature.

I am only even bringing up use of ESS with the main battery because some folks say that's how other car manufacturers do ESS.

Thanks.

 

[58Willys]

Your batteries are probably failing. The only way to know for sure is load test both batteries separately. Harbor Freight sells a cheap load tester, probably sufficient to give you a good idea of your batteries.

 

[58Willys]

It's my understanding that the voltage reading displayed on the dash is not the battery voltage but the voltage output of the alternator. A low reading (12.5-13.5) means your batteries are more or less fully charged, the higher the reading (14.0+) means it's working to charge the batteries
Someone can correct me if I'm wrong.

Essentially you are correct.

 

[andy29847]

The vehicle voltmeter is not a reliable source for testing batteries. The reason is that the batteries are still under some load.

The ESS and the AUX switches are not controlled by the AUX battery, These features are turned on or off according to parameters set by the Jeep system, primarily battery voltage as read by the system.

Deleting the AUX Battery was the path I took. I used the Jumperless method, i.e., I removed fuse F42 and removed the AUX Battery negative cable from the main battery. The Aux Battery negative cable needs to be insulated after removal. I replaced the 2 batteries with a single AGM H7 battery from Walmart. Walmart's best H7 battery has nearly the same power as the 2 Mopar batteries and comes with a 4 year warranty. All of the systems on the truck function the same as if you have 2 batteries.

If you decide to stick to a 2 battery system, you should replace both batteries at the same time.

 

[signals34]

Having read several highly informative posts about AUX battery issues on this forum, I strongly suspect I too am victim of the same. I thought I will share my symptoms and seek second opinion.

Do you concur, the following behavior most likely indicates a failing Aux battery?

1. 2021 JLU Willy's, 2.0 with ESS, 32K miles, just out of warranty (sigh).
2. ESS has not worked for a while already.
3. AUX switches not available warning has been coming up lately, they do become available after about 30s of driving.
4. Per the dashboard screens, the primary batter maintains 12.4-12.6v in Acc mode and 14v+ in full ignition.
5. As such had no issues till this past weekend when I went offroad/camping.
6. At camp, the Jeep was not turned on (ignition) for about 48 hours. It was very cold. Doors were opened closed several times for normal camp style use. I even slept in it. When I tried starting the Jeep after those 48 hours, it wouldn't start. I had to jump it. It started fine after that.
7. But now, everytimeI start it, I have the Jeep warning me about ESS needing service, in addition to the AUX switches not being available.
8. On occassion, when I have the Jeep engine running, and the doors are opened to let someone out, I get key fob has left the Jeep warning. This has happened a couple.of times.
9. The main battery still looks fine from the dashboard screens.

Is my Aux battery failing? Could it have been responsible for draining my main battery?

Thanks.

i had same warnings....just bypassed the aux, left the old one in, replaced the main battery...its perfect now, no issues...

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