Dead Battery

[Lost1wing]

I'm wondering why anyone would actually want to replace their aux battery? What purpose does it serve beyond causing problems? You can't tell if one of the two batteries has gone bad without disconnecting them, and if one dies prematurely, it will tank the other one shortly afterwards... and a bad battery can/will/does blow N3, eventually leaving the vehicle disabled, potentially in the middle of the road because of the ess.

As soon as the warranty is up, that aux battery loop is getting bypassed.

The main function of the Aux battery is to prevent a voltage drop to the electronics during an ESS stop event. Another function is to provide power for cabin essentials during a stop event. Eliminating the Aux Battery will not cause any issues as long as you use Tazer or a disabler for ESS. Leaving ESS active with the Aux battery removed is setting yourself up for issues to arise. Sure, everything will work as normal, that is until your main battery starts to fade.

Sponsored

 

[Geoarch]

Blame BMW - they invented the thing and the system.

BMW did invent it, but in my 2014 Z4, when you pushed the disconnect button, it stayed disconnected. Maybe it's not that way now, but it saved me from always pushing my JTR when I get in.

 

[Dp7]

Leaving ESS active with the Aux battery removed is setting yourself up for issues to arise. Sure, everything will work as normal, that is until your main battery starts to fade.

I guess my point is that leaving the aux battery in place can be more problematic, ESS or not... Whereas the odds are much greater that a weak main battery and no aux will more often than not just cause an "ESS unavailable" state.

I'd much rather have a weak battery that I can jump start, turn ESS off, drive to a Walmart to buy a new battery and be on my way with a few minutes and a socket wrench.... Versus an aux battery that's not as readily available, a giant pain to access, blows fuses you can only get at a Jeep dealer that leaves your vehicle disabled and accelerates the failure of your main battery.

 

[ShadowsPapa]

and if one dies prematurely, it will tank the other one shortly afterwards... and a bad battery can/will/does blow N3, eventually leaving the vehicle disabled

No it won't necessarily tank the other battery. Those of us who have run tractors and other things with multiple batteries can attest to that. We've had one battery go bad, the rest were fine, and you replaced the bad battery before things got cold and you really needed the cranking power (depending on how things were wires - series, parallel, or series/parallel)
There's a lot of multi-battery arrays where one can fail and not kill the other battery - meaning not ruin or destroy it. Depends on how the one goes bad.

the bad battery typically doesn't blow N3 - that's almost always someone replacing the main battery who blows that.
Unless that bad battery "shorts", there's no reason for it to blow that fuse. It's a 150 amp, takes a heck of a lot to blow it.
It's typically the owner swapping the main that blows N3.
That aux, unless shorted, isn't going to take out N3 - it won't take that much current.

The main function of the Aux battery is to prevent a voltage drop to the electronics during an ESS stop event. Another function is to provide power for cabin essentials during a stop event. Eliminating the Aux Battery will not cause any issues as long as you use Tazer or a disabler for ESS. Leaving ESS active with the Aux battery removed is setting yourself up for issues to arise. Sure, everything will work as normal, that is until your main battery starts to fade.

When/if, I get some time, uninterrupted, to do a deep study on the wiring, I'd like to map out exactly which battery powers what.
The reason I say that is - things like the fan and EHPS are powered directly from the main, and I've proven quite a few other things are as well, even during an ESS stop.
I have connected a volt meter to the main battery directly, and one to the aux battery using N1. I've monitored during multiple ESS stop events and noted that the main battery voltage falls almost in lock-step with the aux battery voltage. Not exactly, but the voltage of the main drops enough that I figured perhaps the HVAC fan, among certain other things, may be powered by the crank battery.
Think of the differences in capacity between the two - there must be some decent load on that crank battery to drop voltage from 12.7 to 12.1 volts during an ESS stop - again, that's with the Fluke meter connected directly to the main battery posts.

 

[Lost1wing]

No it won't necessarily tank the other battery. Those of us who have run tractors and other things with multiple batteries can attest to that. We've had one battery go bad, the rest were fine, and you replaced the bad battery before things got cold and you really needed the cranking power (depending on how things were wires - series, parallel, or series/parallel)
There's a lot of multi-battery arrays where one can fail and not kill the other battery - meaning not ruin or destroy it. Depends on how the one goes bad.

the bad battery typically doesn't blow N3 - that's almost always someone replacing the main battery who blows that.
Unless that bad battery "shorts", there's no reason for it to blow that fuse. It's a 150 amp, takes a heck of a lot to blow it.
It's typically the owner swapping the main that blows N3.
That aux, unless shorted, isn't going to take out N3 - it won't take that much current.



When/if, I get some time, uninterrupted, to do a deep study on the wiring, I'd like to map out exactly which battery powers what.
The reason I say that is - things like the fan and EHPS are powered directly from the main, and I've proven quite a few other things are as well, even during an ESS stop.
I have connected a volt meter to the main battery directly, and one to the aux battery using N1. I've monitored during multiple ESS stop events and noted that the main battery voltage falls almost in lock-step with the aux battery voltage. Not exactly, but the voltage of the main drops enough that I figured perhaps the HVAC fan, among certain other things, may be powered by the crank battery.
Think of the differences in capacity between the two - there must be some decent load on that crank battery to drop voltage from 12.7 to 12.1 volts during an ESS stop - again, that's with the Fluke meter connected directly to the main battery posts.

Besides the starter, the main is connected to the powersteering pump. You are correct and I assume you already knew this. When the steering wheel is turned during an Ess stop, the engine should start, ess msg steering wheel turned and ehps should start. I thought I have read that the hvac runs off of the aux during an ess stop event. That is the secondary purpose of the Aux battery according the the manual. I will look at the wiring manual to see it for myself.

 

[ShadowsPapa]

Besides the starter, the main is connected to the powersteering pump. You are correct and I assume you already knew this. When the steering wheel is turned during an Ess stop, the engine should start, ess msg steering wheel turned and ehps should start. I thought I have read that the hvac runs off of the aux during an ess stop event. That is the secondary purpose of the Aux battery according the the manual. I will look at the wiring manual to see it for myself.

One of the over 2 dozen items related to ESS stops is the steering wheel angle, so it would restart if the wheel is turned, or not stop if the angle is too great (I don't recall the degrees, it's a 'greater than xx degrees true/false' check.

I've always "read" that the HVAC fan runs off the aux as well, but that's a pretty large draw, making me wonder if "what I read" is just internet lore or guess-work passed along when 1 person posted that years ago, or if it's a fact based on the wiring diagrams.
I'd have to dig into the diagrams.

But there's something pulling on the main/crank battery during an ESS stop even because it takes some amps to draw down the bigger battery from 12.7 to 12.1 or 12.2 in a minute or so.

If the EHPS pump isn't running (and it won't be) during a stop, then there's some other large draw or a combination of draws adding up.

If you dig into it before I get a chance - I'd be interested in what you find that is connected directly to the main/crank battery when the PCR is opened.

 

[Dp7]

No it won't necessarily tank the other battery

the bad battery typically doesn't blow N3

Sure, these things won't happen 100% of the time... but they can and do happen. Keep in mind that the Mopar batteries are generally regarded as junk. Swapping them out to something maybe higher quality might reduce the chances of catastrophic failure. Either way, I think it's safe to say that the aux battery setup is more likely to cause a problem than a single battery setup, simply because there are more things that can fail. If you know what you're doing, you can move some cables around to "field bypass" the aux setup if your N3 blows... but you only get one shot at guessing the problem because only N4 is viable to limp along with...

My N3 fuse blew several times this year after replacing the aux battery and starter and PCR until the main battery was determined to be the cause of the problem - even though it tested good. Anyway.. the point is, N3 blowing aint always user error. How common is it? Well.. I suspected it was the main battery before the shop changed it out because I read about other people having the same problem on forums..... so, it must be more common than just me.

 

[Lost1wing]

One of the over 2 dozen items related to ESS stops is the steering wheel angle, so it would restart if the wheel is turned, or not stop if the angle is too great (I don't recall the degrees, it's a 'greater than xx degrees true/false' check.

I've always "read" that the HVAC fan runs off the aux as well, but that's a pretty large draw, making me wonder if "what I read" is just internet lore or guess-work passed along when 1 person posted that years ago, or if it's a fact based on the wiring diagrams.
I'd have to dig into the diagrams.

But there's something pulling on the main/crank battery during an ESS stop even because it takes some amps to draw down the bigger battery from 12.7 to 12.1 or 12.2 in a minute or so.

If the EHPS pump isn't running (and it won't be) during a stop, then there's some other large draw or a combination of draws adding up.

If you dig into it before I get a chance - I'd be interested in what you find that is connected directly to the main/crank battery when the PCR is opened.

The engine cooling fan fan is the other large draw from the main battery. N5 and n6 are for the cooling fan and powersteering. That is all I see on the main during an ESS. If you look at the hvac controls diagram , it does not specify the aux or the main. If you look at the cooling system it does show power for the fan direct from the main and control from the aux. For the ehps they don't specify n2 or n1, but I suspect it works the same as the cooling system. N2 direct to the pump n1 for control. This wiring diagram is more like a schematic.

 

[ShadowsPapa]

EHPS is N6. That line goes right to the pump. What controls the pump would come from the BCM, via the fuse panel.
If you short the wire leading to the pump, you'll blow, or hopefully/should blow, N6.
N6 is directly on the main bus from the main/crank.
So it's from main + to the high current fuse array bus bar, out through N6 directly to the pump.
That part I've got.

N5 is the fuse for the fan and also comes directly from the battery +.

So there's a cable running from N5 to the fan controller and on to the fans.

Power comes directly off the main + to the bottom of the high current fuse array - via N2, then out through each fuse in the array.
The main battery + goes to N2, which is a direct connection, not fused, to the array bus.
N2 connects to the bus as shown by the arrow, there's no fuse where the "0698" numbers are printed in this example.
So anything fed through this array, gets power very directly from the crank battery.

 

[ShadowsPapa]

Sure, these things won't happen 100% of the time... but they can and do happen. Keep in mind that the Mopar batteries are generally regarded as junk. Swapping them out to something maybe higher quality might reduce the chances of catastrophic failure. Either way, I think it's safe to say that the aux battery setup is more likely to cause a problem than a single battery setup, simply because there are more things that can fail. If you know what you're doing, you can move some cables around to "field bypass" the aux setup if your N3 blows... but you only get one shot at guessing the problem because only N4 is viable to limp along with...

My N3 fuse blew several times this year after replacing the aux battery and starter and PCR until the main battery was determined to be the cause of the problem - even though it tested good. Anyway.. the point is, N3 blowing aint always user error. How common is it? Well.. I suspected it was the main battery before the shop changed it out because I read about other people having the same problem on forums..... so, it must be more common than just me.

If people know what they're doing, they'd jump from N1 to N2 and skip the fuse. N1 isn't fused power anyway. I don't know why people would go to N4. No need for a fuse.
...........unless of course the aux battery is shorted, then you can pull the aux battery ground to resolve that issue. Or use a fused jumper if worried about it.
And all you need for that is a large alligator clip. It's so simple.

Be careful what you glean from forums - a lot of it is guesswork from people who kept trying things until it worked then figured "this is the solution" or blamed things they didn't understand.
More often than not they have no clue what's fed from where or why.

I've been in automotive electric for over 50 years and the craziness out there that passes for fact just baffles me.

I've written up a ton of info on these systems over the years here - with Jerry's help finding the original simple diagrams, of course.

 

[Dp7]

If people know what they're doing, they'd jump from N1 to N2 and skip the fuse.

I've looked at that and I keep thinking the 150amp fuse must be there for a reason... since your entire system electronics are effectively routed through that N3 fuse to N1, I feel like running unfused straight to the main battery could be bad.

Edit: I guess I keep thinking in terms of bypassing the aux battery and the main battery only getting to the system electronics through N3... but, yeah since the aux battery is unfused to N1, I guess it shouldn't matter?

Edit 2: Makes me wonder why the aux is fused at all... main battery isn't fused, what's it even there for?

 

[Blade1668]

Well, a update on some of the things a dead shorting ESS battery will do. Fry the main fuse bar in the vehicle.

This has to be replaced and the new batteries have been discharged (to 4v from 13.7) by the vehicle going into run with it trying to cycle everything without any input. "By the time I got it off rollback it was down to 10.3v." This was the update I got on Friday after being at dealership since Tuesday. At earliest Monday more likely Tuesday. BTW the batteries were from Nov. 2019, made in Brazil most likely. That's from information printed on batteries.

 

[jeepers29]

On my way home from Colorado, driving down the road, I got the service start stop soon message. My 21 Mojave has been on a maintainer almost since new when not being driven. The truck is 3 years and a half month old. These batteries are crap. I will be replacing both and fully charging them before I install them. Frustrating, as I thought the maintainer would give me some extended life.

 

[Mr._Bill]

On my way home from Colorado, driving down the road, I got the service start stop soon message. My 21 Mojave has been on a maintainer almost since new when not being driven. The truck is 3 years and a half month old. These batteries are crap. I will be replacing both and fully charging them before I install them. Frustrating, as I thought the maintainer would give me some extended life.

The OEM batteries are crap. You did well to get the three years out of them. The maintainer kept them from dying sooner. Using the maintainer should help get a longer life out of the new batteries.

 

[g2020]

For price comparison:
Installed on December 16, 2024
$488 total w/ 15% discount and incl tax, for both MOPAR batteries installed by a dealer in Texas
Storage battery (MOPAR BBH6A001AA)
Auxiliary battery (MOPAR BBAUX101AB)
40-month warranty
Same-morning service (about three hours)
2020 Gladiator Sport 3.6L V6 Automatic, no mods

Tip on two charging posts for auxiliary battery:
- 5/32" socket, to remove & install charging posts
- 4 mm socket will also work (only 1/1000th of an inch larger than 5/32" socket)

For access to the auxiliary battery, see how to remove & reinstall the right front splash shield.

Sponsored