New Batteries still 15.1v when running

[ImAJeepskate]

I have just replaced my main and Aux battery a week ago and since then I have still been reading 15.1v at idle and speed while driving. It's a 3.6 without eTorque. Is my alternator failing? Anything else in this "not so smart" charging system?

Sponsored

 

[Heimkehr]

That charging voltage is too high and definitely worth a deeper dive.

Just off the top of my head, yes, test the alternator in isolation and go from there.

Related: The same 15.xV charging voltage displayed on the affected motorcycle's voltmeter eventually pointed me to a failing OEM regulator/rectifier. Replacing it with a well-regarded MOSFET R/R upgrade solved the issue. So, again, this'll be worth your time to reconcile.

 

[THAW]

Consistent 15.1 V is high, definitely something to investigate.

Keep in mind, though, below freezing Minnesota temperatures are relevant, and IBS recalibration (due to battery disconnection) takes significant time and multiple ignition cycles.

 

[Heimkehr]

Keep in mind, though,...IBS recalibration (due to battery disconnection) takes significant time and multiple ignition cycles.

I've not noticed that. I have to date disconnected my battery twice in almost as many months: a little while ago, when I replaced the original H6 with a new H7, and then ~1 week ago when I isolated the ESS battery. That involved removal of the corresponding Negative cable (which meant removal of both Negative cables for a few minutes, causing a full power disconnection) and the related Fuse F42.

In both instances, both the battery and by extension the IBS were reconnected after just a brief interval. There wasn't any wonkiness or anything else that occurred to suggest that a recalibration of any sort was needed or occurring. The initial restarts occurred without delay or issue.

Possibly such things depend on the vehicle's trim, and/or what the owner has added to it?

 

[THAW]

I've not noticed that. I have to date disconnected my battery twice in almost as many months: a little while ago, when I replaced the original H6 with a new H7, and then ~1 week ago when I isolated the ESS battery. That involved removal of the corresponding Negative cable (which meant removal of both Negative cables for a few minutes, causing a full power disconnection) and the related Fuse F42.

In both instances, both the battery and by extension the IBS were reconnected after just a brief interval. There wasn't any wonkiness or anything else that occurred to suggest that a recalibration of any sort was needed or occurring. The initial restarts occurred without delay or issue.

Possibly such things depend on the vehicle's trim, and/or what the owner has added to it?

Fully disconnecting 12V power will reset the IBS. I'm not suggesting doing so will necessarily cause wonkiness, in most cases it won't. But, erasing cumulative IBS data and installing batteries when ambient temperature is below freezing could result in higher than typical charging voltage.

 

[Jebiruph]

I'm seeing more 15.1 V charging now that I'm watching it after the clutch recall software update and colder weather started. It used to never go above 14.8 V.

 

[The Last Cowboy]

If you didn’t charge the batteries to 100% prior to installing, you may want to do that. Especially if all your trips are short.

Or you can take it out for a good highway drive of about an hour to get them fully charged.

 

[ImAJeepskate]

I'm seeing more 15.1 V charging now that I'm watching it after the clutch recall software update and colder weather started. It used to never go above 14.8 V.

This is my first winter after the clutch recall. interesting

 

[mijlur]

Have you verified the voltage with a multimeter or just going by dash info?

 

[Jebiruph]

This is my first winter after the clutch recall. interesting

It looks like the firmware update also increased the charging voltage.

 

[Nokones]

Most new batteries are not fully charged and the new later Jeeps do require a higher power draw/load. I would put your new battery on a quality smart charger and see what happens after it is charged. If the charger continues to charge and not move to the maintain state in a reasonable amount of time, it is possible that the battery may have failed from out of the box so to speak.

What year model is your Jeep? Hopefully, you replaced your battery with the OEM battery or equivalent battery in capacity and battery chemistry and not with a cheap discounted battery from a cheap retailer. The battery chemistry has to match what the alternator output profile is designed for. In other words, if your OEM battery is a lead acid wet cell that means the alternator output profile is designed for only lead acid batteries not for AGM batteries that require a different voltage rating and charging algorithm.

 

[Fleeclan]

I have just replaced my main and Aux battery a week ago and since then I have still been reading 15.1v at idle and speed while driving. It's a 3.6 without eTorque. Is my alternator failing? Anything else in this "not so smart" charging system?

Not assuming you don’t already know this but the voltage while running is sole responsibility of your alternator assembly. I say assembly because the voltage regulator is an integral part of your alternator. Years ago automobile alternators did have external voltage regulators but modern alternators have built in voltage regulators. A very weak battery will cause the regulator to put out a higher voltage than when normally maintaining a well charged battery but 15.1 is too high. That will negatively affect your new batteries and eventually cook your new batteries.
Check the voltage at the battery with a digital meter with jeep running and see what your reading is. 13.5-14.5 is the range you should be looking for.

 

[garykk]

Whatever the reason, over 15 volts will damage your battery.
When I deleted the Aux. And replaced the main with an H7, I made sure the new battery was fully charged but even then the charging volts jumped around for about a day or so until the IBS recalibrated.

 

[ImAJeepskate]

I have charged both batteries directly overnight and disconnected the sensor from all power. Will drive around for the next few days and see if things recalibrate properly and update.

 

[Jebiruph]

The charging voltage is determined by the PCM, not the battery.

Sponsored