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Alternator or battery?

Fpolanco

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2021 Mojave that I bought June 2021. Been recently having some charging issues and wanted to get some feedback before I start the process of talking to the dealer.

I start the Jeep and voltage meter reads btwn 13.4 and 13.6 v. I don’t know much I know that’s pretty low for a relatively new vehicle.

Even after driving for 30+ min, the meter will read btwn 13 and 13.2, sometimes dropping as low as 12.9. Here’s where it gets confusing...

Under load (acceleration and crushing), the reading will dip to btwn 12.9 and 13.2. However, if I coast to a stop, the reading jumps to 13.7 or 13.8.

I currently have the 4 ga wire that powers the compressor in the bed on a kill switch, which is off until I need to use it. The only other accessories I have wired to the battery are the winch and the Baja Designs fog lights (which are on a relay and I still use the OEM fog light switch).

Before I start disconnecting all accessories, anyone have any other ideas?
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It's possibly the ESS battery starting to fail. You can hassle the dealer for battery testing and replacement, or swap it out yourself.
 

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Are you getting any sort of error or just the abnormal reading?

There are a number of factors to consider here, including the fact that the ecm controls how much the alternator powers the battery. Modern vehicles have smart alternators, keep that in mind.

Another thing to consider is a myriad of bad batteries Jeep put in these trucks for the 2020 and 2021 model years, if you are having issues and/or drivability issues, look into that at your service center.
 

ShadowsPapa

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2021 Mojave that I bought June 2021. Been recently having some charging issues and wanted to get some feedback before I start the process of talking to the dealer.

I start the Jeep and voltage meter reads btwn 13.4 and 13.6 v. I don’t know much I know that’s pretty low for a relatively new vehicle.

Even after driving for 30+ min, the meter will read btwn 13 and 13.2, sometimes dropping as low as 12.9. Here’s where it gets confusing...

Under load (acceleration and crushing), the reading will dip to btwn 12.9 and 13.2. However, if I coast to a stop, the reading jumps to 13.7 or 13.8.

I currently have the 4 ga wire that powers the compressor in the bed on a kill switch, which is off until I need to use it. The only other accessories I have wired to the battery are the winch and the Baja Designs fog lights (which are on a relay and I still use the OEM fog light switch).

Before I start disconnecting all accessories, anyone have any other ideas?
No, that's not relatively low.
Depending, these will go as low a upper 12s. Mine has gone 12.7.
There's a TSB on this telling people it's NORMAL.

These control alternator output based on need. These are not regulated like the old day to a set voltage.
As long as your voltage is actually fluctuating like that, it's likely fine.
Not sure where you found the "relatively low for a new vehicle".


Anything you add to the Jeep, make sure the ground comes from either the body ground studs or the top of the IBS - never charge directly to the negative battery post, never pull directly from the post.



This is normal if the system finds the batteries at capacity and the electrical load needs are low. It's to cut power robbing charging when it's not needed.

In the past the alternator was a parasite even when not needed.


Jeep Gladiator Alternator or battery? 20210613_150145
 

ShadowsPapa

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Modern vehicles have smart alternators, keep that in mind.
Actually, Jeep doesn't use the smart alternators on these - it's done via the IBS and PCM.

When the PCM determines the batteries are fully charged, when the IBS reports 100% SoC, and the load is relatively low, the PCM cuts field current to save power and fuel.
It tracks every milliamp going in and coming out.
 

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Jefe1018

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Actually, Jeep doesn't use the smart alternators on these - it's done via the IBS and PCM.

When the PCM determines the batteries are fully charged, when the IBS reports 100% SoC, and the load is relatively low, the PCM cuts field current to save power and fuel.
It tracks every milliamp going in and coming out.
I stand corrected, thanks! Same concept, but a different delivery method I suppose.
 

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I stand corrected, thanks! Same concept , but a different delivery method I suppose.
Yeah, it's the same sort of thing.
Either way, the results should be the same.
Cut parasitic draw of an alternator that's not needed at that time, vary output based on need and load more than regulating to a set voltage no matter what.

When mine first showed 12.7, or rather when I first saw it at 12.7, I noticed we were tooling down the interstate at about 80 so cooling fans weren't really needed, it was NE so there was almost nothing for hills, it was daytime so no lighting load, etc.
 

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Fpolanco

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No, that's not relatively low.
Depending, these will go as low a upper 12s. Mine has gone 12.7.
There's a TSB on this telling people it's NORMAL.

These control alternator output based on need. These are not regulated like the old day to a set voltage.
As long as your voltage is actually fluctuating like that, it's likely fine.
Not sure where you found the "relatively low for a new vehicle".


Anything you add to the Jeep, make sure the ground comes from either the body ground studs or the top of the IBS - never charge directly to the negative battery post, never pull directly from the post.



This is normal if the system finds the batteries at capacity and the electrical load needs are low. It's to cut power robbing charging when it's not needed.

In the past the alternator was a parasite even when not needed.


Jeep Gladiator Alternator or battery? 20210613_150145
I’ll triple check but the only thing I have connected to the negative post of the battery is the winch. Everything else is on those studs on the body near the battery.

Should I move that winch wire to those posts?
 
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Fpolanco

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Yeah, it's the same sort of thing.
Either way, the results should be the same.
Cut parasitic draw of an alternator that's not needed at that time, vary output based on need and load more than regulating to a set voltage no matter what.

When mine first showed 12.7, or rather when I first saw it at 12.7, I noticed we were tooling down the interstate at about 80 so cooling fans weren't really needed, it was NE so there was almost nothing for hills, it was daytime so no lighting load, etc.
Your previous few replies make me feel better.

I was just concerned b/c we have a trip to Colorado coming up in July and I don’t need to get stranded anywhere.

Plus the combo of the bad batches of batteries and my friend’s Gladiator charging at north of 14v had me concerned too.

Thank you!
 
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Fpolanco

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It's possibly the ESS battery starting to fail. You can hassle the dealer for battery testing and replacement, or swap it out yourself.
I’m an idiot when it comes to this so I apologize...but the ESS battery is the smaller one that’s a giant PIA to change, right?
 

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ShadowsPapa

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The idea is to take negative not from the negative post itself, but from above the IBS, or a body connection.
I have my winch negative on the stud on top of the IBS.

Jeep Gladiator Alternator or battery? JT-neg-bat-post-connect
 

ShadowsPapa

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I’m an idiot when it comes to this so I apologize...but the ESS battery is the smaller one that’s a giant PIA to change, right?
Yeah, it sure is.
I'd not sweat it as long as things are working.
I posted the bulletin above in another post in this thread.

I was coming back from Colorado Springs when I first noticed mine at 12.7 volts.


Jeep Gladiator Alternator or battery? 1653180181155
 
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Fpolanco

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The idea is to take negative not from the negative post itself, but from above the IBS, or a body connection.
I have my winch negative on the stud on top of the IBS.

Jeep Gladiator Alternator or battery? 1653180181155
Oh oh gotcha. Yeah I’m pretty sure I have that set up properly but I’ll check again tomorrow morning.
 
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Fpolanco

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Yeah, it sure is.
I'd not sweat it as long as things are working.
I posted the bulletin above in another post in this thread.

I was coming back from Colorado Springs when I first noticed mine at 12.7 volts.
Is there a “standard” anymore of what the voltage should read first thing in the morning? I’ve always been taught the battery should read at least 12.4v.

I’m coming from a 2008 JKU so my basis for understanding is somewhat “old school” at best...
 

ShadowsPapa

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When I first start mine it's in the 14s, sometimes 13s. Mine has been sitting a lot lately to save miles on it (I have it traded in for a new one) so the battery itself reads low.
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