On this episode of "Batteries gone bad"

[Mball488]

So, like most of ya'll I've hit the 3 year anniversary to the F'ing day of purchasing my 2020 JTR. It was like every other morning, went to the garage, hopped in and noticed a weak start. As I was backing down the drive way the infamous Auto start (ESS) light popped up on the dash. I knew this day was coming eventually since MOPAR I'm pretty sure programs everything to go wrong the day of their expiration dates. So I pop down to the local auto parts store and make sure that I got the right or equivalent AUX14 battery to do the swap. When I got the new one to the house I popped it on the battery charger and just topped it off at 1.5 amps. This evening I swapped the Aux battery from the fender and proceeded to run some errands after. The light remained on and after about an hour or so of driving I noticed it just didn't go off. I went to the Batt page on the dash and noticed my main battery at 12.7 volts. Correct me if I'm wrong, but shouldn't it be around 13-13.5 while the alternator is doing its job? Any who, I got home and put the main battery on the charger as well and waited a few hours. It got to 14.4 on the charger but when I went to start again it showed 12.7 then dropped to 12.5. Does this mean that the main isn't holding its charge and I need to replace it? The damn auto start light is still lit up like an xmas tree on my screen! Suggestions would be amazing.

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[Andy29847]

It's not that simple. The batteries need to be separated to be properly tested. I expect that your main battery is weak and needs to be replace. IMHO, the batteries should be replaced in pairs.

 

[ShadowsPapa]

So, like most of ya'll I've hit the 3 year anniversary to the F'ing day of purchasing my 2020 JTR. It was like every other morning, went to the garage, hopped in and noticed a weak start. As I was backing down the drive way the infamous Auto start (ESS) light popped up on the dash. I knew this day was coming eventually since MOPAR I'm pretty sure programs everything to go wrong the day of their expiration dates. So I pop down to the local auto parts store and make sure that I got the right or equivalent AUX14 battery to do the swap. When I got the new one to the house I popped it on the battery charger and just topped it off at 1.5 amps. This evening I swapped the Aux battery from the fender and proceeded to run some errands after. The light remained on and after about an hour or so of driving I noticed it just didn't go off. I went to the Batt page on the dash and noticed my main battery at 12.7 volts. Correct me if I'm wrong, but shouldn't it be around 13-13.5 while the alternator is doing its job? Any who, I got home and put the main battery on the charger as well and waited a few hours. It got to 14.4 on the charger but when I went to start again it showed 12.7 then dropped to 12.5. Does this mean that the main isn't holding its charge and I need to replace it? The damn auto start light is still lit up like an xmas tree on my screen! Suggestions would be amazing.

Why did you jump to the conclusion that the issue was the aux battery -with no testing, especially? Because the internet says so, I'm guessing.
Could be both or the main.

You replaced the aux battery - it's possible a fuse was blown in the process if things weren't totally separated cable-wise

Anyway -
You need to chare each battery separately.
Do a full charge - a real AGM charger - more than an amp.
Do both, one at a time.
Ensure they settle to at least 12.7 or 12.8.

You'll want to check after a few hours and see that they hold the charge and not drop (leave disconnected, if possible)

You should see running voltages higher than 12.7 when the engine is running. If you don't, you have a problem with the high current fuse or charging system.
in fact that could be the whole reason you saw problems to begin with.

 

[ShadowsPapa]

Everyone should look at this video before jumping to replacing stuff. (and it's not always the aux battery that causes the issues)



https://www.jeepgladiatorforum.com/...-those-batteries-just-yet.74283/#post-1211885

 

[Mball488]

Shadow, yeah I put each of them on my AGM Charger, the Aux only went to 9.1V and the main never got above 12.8, then the charger would show 10-11 and fluctuate voltage for a min then drop it back down. Im going to check all the fuses and everything in the morning to see if that might be the case for running the batteries down so much.

 

[SoK66]

This setup is similar to replaceable batteries in a flashlight. It may be that only one of them is in its death throes, but you should replace both at the same time. One on its way out will slowly kill the other.

There's a lot of “Internet wisdom” on this subject, a lot of it just jumping to conclusions. I don’t like the design or the ESS feature myself but it’s best to just live with it. Heaven knows what will happen long term with pulled 42 fuse, aux battery removed & the circuit bypassed, etc. Maybe nothing, but as integrated and complex as these systems have become it's a potential Big Bang if you screw it up.

 

[DaleG]

both of mine died within a month of each other (aux killed main)…..2 months out of warranty….?

 

[JTGuy]

I see the batteries as a package. One goes and they both get replaced. If one goes the other is close behind and you are just wasting time not to do both at the same time. The question is what ones to get? The two battery system is just added operating cost. The simple days are gone.

 

[Mball488]

So I have resolved it. I replaced the main battery today and all is well. I did look at the fuse box and holy crap. Almost every single fuse was super loose!

 

[Outback_Joe]

I am asking a question on how two different sized batteries can be on the same charging circuit and live long happy lives together.

Back in the day, large tucks, and heavy off road equipment had 4-6 volt batteries. We never changed just one we changed all of them and made sure they were a matched set. I don't see how two such drastically different sized batteries are every going to go the distance with no real and complete separation as these are bonded to each other at different times and at different discharged states.

I think that someone was selling some real (EPA) BS to the design team when this type of storage system was installed on our vehicles. Its a marriage made in hell from a design standpoint.

 

[Mr._Bill]

I am asking a question on how two different sized batteries can be on the same charging circuit and live long happy lives together.

Back in the day, large tucks, and heavy off road equipment had 4-6 volt batteries. We never changed just one we changed all of them and made sure they were a matched set. I don't see how two such drastically different sized batteries are every going to go the distance with no real and complete separation as these are bonded to each other at different times and at different discharged states.

I think that someone was selling some real (EPA) BS to the design team when this type of storage system was installed on our vehicles. Its a marriage made in hell from a design standpoint.

The two batteries are paralleled together all the time, except during the startup test and during ESS events. The two battery setup is intended to keep marginal batteries from causing the computers to reboot from low voltage during ESS events. The design has been in use over ten years, it is not a new Jeep incarnation. The expected lifespan in the JT is about three years, depending on how well the batteries are kept charged. The recommendation is to replace both, when it is time, but not everyone does that.

 

[JTGuy]

Is there a "best" battery mfg for our use?

 

[Mr._Bill]

I like ACDelco, and Interstate is good.

 

[Outback_Joe]

The two batteries are paralleled together all the time, except during the startup test and during ESS events. The two battery setup is intended to keep marginal batteries from causing the computers to reboot from low voltage during ESS events. The design has been in use over ten years, it is not a new Jeep incarnation. The expected lifespan in the JT is about three years, depending on how well the batteries are kept charged. The recommendation is to replace both, when it is time, but not everyone does that.

Understood, batteries should last 7 to 10 years. But with this type of paring that will never happen. Just saying the baby battery is always going take the brunt of abuse in this type of install. Thinking otherwise won't change the way its being abused.

 

[Escape.idiocracy]

This thread has been really helpful.
factory main battery failed the autozone test- 2.5 years old. Figured we just didn’t quite get the full 3 years most others get. Replaced both main and auxiliary. (Stuck both on Chargers before installing to ensure we’re full) duralast platinum agms- September and October manufacturers production date.


Few days later voltage in the cab is reading 12.2-12.3 @ start up. Had a long 150 mile drive for the weekend running voltage fluctuated from 13.6-14.4 (normal- I think). Next day again low 12’s

Pulled both batteries put them on a charger… auxiliary battery was basically full/topped off. Main battery read less than 80%… will leave until full, then leave off the charger for a few hours and will check voltage settled amount.

checked the fuse array- all passed continuity, pulled ALL fuses… ?… micro fuses… checked the canbus plugs under/behind the glove box. So far not finding any “ah-ha’s” -

Almost wondering if we picked up a bad main battery?? As it seems we have the opposite problem to most, in that the auxiliary is charging fine in the car, but not the main…?

Anyone have any other troubleshooting ideas or thoughts that they would like to share?

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