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Hey all. I’ve searched and could not really find any info about my problem. On my 18 limited when I’m cruising down the road doesn’t matter what speed my battery voltage is hovering right around 13.0 or 12.9v. Now the weird thing is when I let off the gas it goes up to 14.4v. When I come to a stop it goes back down to 12.9v and stays there. Has only happened the last 2 days since the weather got a little bit warm. When it’s cold it stays around 14.4v.

I’m gonna verify it with a voltmeter tomorrow morning. Anyone have any ideas. Jeep has 2500 miles on it and I don’t really trust the dealer.


James
 

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2014 Summit 5.7 4wd 20" tires swapped to 18", added all skid plates
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Hey all. I’ve searched and could not really find any info about my problem. On my 18 limited when I’m cruising down the road doesn’t matter what speed my battery voltage is hovering right around 13.0 or 12.9v. Now the weird thing is when I let off the gas it goes up to 14.4v. When I come to a stop it goes back down to 12.9v and stays there. Has only happened the last 2 days since the weather got a little bit warm. When it’s cold it stays around 14.4v.

I’m gonna verify it with a voltmeter tomorrow morning. Anyone have any ideas. Jeep has 2500 miles on it and I don’t really trust the dealer.


James
There have been so many reports of how these jeeps are really sensitive to "low voltage" that I would take it to the dealer pronto before modules start burning out. It doesn't sound normal.. perhaps they forgot to tighten some ground wires.. lots of earlier years were burning up alternators due to faulty ground wires.
 

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Discussion Starter · #3 ·
Not sure it would be any ground wires. But I checked and the ones I could find where tight. If they were loose the change in temp wouldn't cause it to charge more or less just cause the cables were loose.. I'm almost starting to think that maybe it has something to do with fuel economy. ( I know I know I might be sounding crazy here but hear me out.. )

The more load you put on a alternator the harder it is too spin. Harder to spin the engine is working just a tad bit harder to spin it. Maybe just maybe its only putting out enough to cover what the car is using because it can sense the battery is near or at full charge. Sounds crazy I know but I read Hondas are doing this in their civic and accords.. Just a thought. :thumbsup:


James
 

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2018 JGC Limited
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I noticed a similar change while on a road trip 2 weeks ago. I was cycling through the diagnostics after a few hours driving and the charge dropped down to 12.x yet everything was operating fine and I was on the highway.

Forgot about it and then checked later in the day after stopping for a bit and it was at the normal 14ish.

That would make sense if it was lowering the charge rate once the battery was full and the vehicle wasn't using a lot of power.
 

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Most intelligent chargers will dial down the voltage once full charge has been obtained so that they don't boil off the batteries - Full charge of a "depleted" battery will usually be in the 14.5 area and can drop down to the 13.0 territory once battery nears full charge
 

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I will add my experience to this thread.


On a long trip (400+ miles), after a few hours, I noticed that the voltage was at 12.8v when the engine was under power. When coasting down a hill, the voltage went up to 14.4v. When power was added again, it dropped to 12.8v. At a stop idling, it was also 12.8v. I noticed it two days in a row behaving this way - but only after at least an hour of driving (I didn't check the voltage early in the drives).


When I got home, the next day I tested it on some shorter freeway trips of 15 or so miles. Under load this time, it was 13.8v and coasting was 14.4v. Idle was 13.8v.


I don't know if it drops down to 12.8v after a set amount of time or not. I'll need to do some more testing with longer drives to find out.


I agree with the post above that this may be related to fuel savings from reducing the alternator load when a battery is fully charged. But, 12.8v seems too low. I've always been taught that anything under 13.2v is discharging the battery. So 12.8v on a long drive like the ones I took could be draining the battery (theory, not proven...).


Has anyone taken their GC to the dealer with this issue and received their explanation? Or any experts around that can confirm if this is expected and designed to work this way? I'm concerned because I've seen reports of batteries going dead after 2.5 years, which sounds early. And if the system doesn't charge them sufficiently in certain cases, that could be why.
 

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2018 Jeep GC 4x4
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You do not have a problem and your system is operating normally. My 2018 GC electrical system behaves in a similar manner. I also had the same questions when my 2016 Charger Scat Pack did the same thing. A 31 year MOPAR tech on a Charger Forum explained to me what was happening. See attached PDF.
 

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That's good to know, thanks for the reply and the attachment! The functionality explained makes sense.

The one question I still have is around the 12.8v level I experienced. In your PDF it seems to indicate that low 13's is the low point when charging a "warm" battery while in a fuel saving mode. Is 12.8v too low? I searched around for information on that and found this article on the Optima battery site talking about AGM batteries (I'm assuming we have AGM batteries and not "standard" flooded lead-acid batteries).

https://www.optimabatteries.com/en-us/support/charging/recommended-battery-voltage

This says: "Fully charged, engine not running, starting batteries (all REDTOP® or BLUETOP® 34M) should measure about 12.6 volts to 12.8 volts."

Which, to me, says that 12.8 volts isn't too low for a fully charged battery, as it's not discharging at that voltage.

Thanks again!
 

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2014 Summit 5.7 4wd 20" tires swapped to 18", added all skid plates
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You do not have a problem and your system is operating normally. My 2018 GC electrical system behaves in a similar manner. I also had the same questions when my 2016 Charger Scat Pack did the same thing. A 31 year MOPAR tech on a Charger Forum explained to me what was happening. See attached PDF.
Amazing the lengths they go to in order to eke out another 0.03% gas mileage. I guess every little bit adds up.
 
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