[Yawnie'sPapa]

So this booster i bought only has On and Off. Should I return it and get something different?

You have to overcome the dead battery. That means either charging it, or using a booster that's so large it can overcome the dead battery and bring the battery voltage up. If the battery is 750 cca or xx amp hours, you have to have a booster that can literally charge such a battery. Boosters/jump packs are for cranking the conventional starter on a gas engine, not recharge a dead battery. Most won't have that much capacity.
Buy a good AGM battery charger, you'll be better off.

 

[Yawnie'sPapa]

Thanks folks. I exchanged the Super Start booster for a Schumacher 15a AGM-compatible charger. Plugged it in and the readout told me the battery was at 3.3V. So that's going to be plugged in for a few hours.

Hopefully this works. The electronic parking brake is on, it's backed into my garage and it's really awkward to get in and out because of the limited space in the driveway. Towing it out will be interesting if it comes to that.

Wow! Well, if nothing else, now you have a number to go along with it - 3.3 volts is a very drained battery and explains why even a great jump pack wouldn't do the job.

I've been in auto electric for over 50 years, and have a fair understanding of 12 volt systems and batteries but geesh, you are never too old to learn new stuff and these are really proving that to me.

The 15 amp charger should do a good job.
I've had dead batteries in my classics that were assumed to be trashed, but a good charger actually brought them back to life and still using the batteries today.
Maybe........ you can experience some good luck for a change.

 

[Yawnie'sPapa]

There's a procedure in the manual that actually calls for hooking up a battery temporarily to actuate the parking brake.

I don't have the manual handy - but if that 12v battery is still in the mix, won't it kill down any battery that you try to connect to release the parking brake - unless there's some special connection that avoids being in parallel with a dead and parasitic battery?

 

[Yawnie'sPapa]

My apologies everybody if I'm missing something in this thread. It seems like there's a dead 12 volt battery, and we're trying to figure out how to get the car out of the garage to get it to the dealer to put in a new battery.
If that sums it up, why don't we just put in a new battery. My wife has a 21 Grand Cherokee Trackhawk, the 12 volt battery is underneath the passenger front seat. I recently replaced that with a Odyssey AGM battery and while it was a bit of a pain in the rear, it's doable.
Even if the owner is not mechanically inclined, I think it would be easier to call a mobile mechanic or one of those battery services that come out to replace the battery. I guess what I'm getting at is, wouldn't it be easier just to replace the battery where it is since it needs to be replaced anyway?

Three words as to "why not": WARRANTY, PRINCIPAL, DOLLARS
It's under warranty, I'll be @$#$% if I'm going to pay for (and install) a battery they owe me.
It's their job to replace it (I'm a retired long-time auto mechanic, so this would be an easy fix if it wasn't for the above)
It's the principal of the thing - why should I do what they should be doing, spend extra out of pocket dollars?
It's a Jeep defect they need to deal with and if I took care of it myself, then they'd have one less complaint, one less record and one less reason to move forward with fixes. That's why any time there's a defect or warranty issue, make sure it gets reported, make sure Jeep engineering, STAR, whoever, knows of it. You may be helping the next Jeep owner toward a solution. It's not to be mean, it's the way the system works. No complaints, gee, nothing to fix.

Of course, I have it easy - the experience and training and all of the needed equipment, I could drag the beast onto my tilt-bed car hauler and tow it to their dealership and nicely drop it off in a spot that's inconvenient for them so they would have to move it in a short time.

When the batteries in my wife's 2018 WK2 failed, trust me, I did everything necessary to get it started and drove it myself (so she'd not have to deal with it) to the dealership. They were really nice about it and put in two new batteries in short order (I was nice about it, too......... explained exactly how it behaved, or misbehaved)

If this one in question was mine - with very low miles, it would get dragged or driven to the dealership and I'd not take it back until they could prove the whole issue was resolved. I have back and forth - anyone wanting evidence of that look at my 4xe transmission leak issue from last year - I don't put up with incompetence or ignorance, no patience for it)

 

[Yawnie'sPapa]

Here's what the manual has to say
View attachment 12733

The problem with that process is - it won't work with a typical jump pack or ordinary battery because a defective or even totally dead battery will drop the voltage of the jump pack - or other battery, down to nothing, like has been shown here. You must overcome the drain the faulty battery presents. It takes a heck of a jump pack to overcome a dead and possibly shorted onboard battery. They make it look easy - hey, just use a jump pack! Uh, no, battery at 3 volts, connect jump pack, load from bad battery drains the jump pack in seconds.
A running "donor" vehicle at a fast idle is the only way I see through this showing the history of his attempts to use a charger, a jump pack he already tried (and failed), and so on. They are assuming the 12v is just low, low enough to not let the PHEV start, but not so low as to kill any jump pack or donor vehicle.
We see this all the time in the 3.6 ESS world - one battery goes bad and the other is sucked down to nothing at all. Even that little aux battery can suck the life out of the crank battery so bad you can't start it and jump starting is very difficult in some cases - this is like that except instead of a tiny motorcycle size aux battery totally killing the crank battery, you have a full-size 12v battery killing a donor battery or jump pack.
Jeep needs to revisit that text, IMO..
I've seen too many cases where this is going to fail miserably.

 

[Yawnie'sPapa]

100%. I work in computer engineering, so unless you measure fail rates, no one is going to improve it. The other concern is what if another part in the system caused the battery drain? I don't think that's the case here, but I'm not an expert.

Otherwise, I'd be taking it to the mechanic down the street to pull and replace the battery.

I transitioned from being a mechanic full time to IT - when I was at Compressor Controls Corp, I was to put together the computers used as the interface for their new Series IV turbo compressor controllers. I used motherboards from YMS and on occasion needed to chat with them about a few things. Interesting conversations...........

 

[Yawnie'sPapa]

seriously? the tech didnt know how the 4xe worked?

Makes sense - it's a complex vehicle and it takes time to learn - and if the dealership doesn't sell many if any of the 4xe, there's little incentive for them to pay for training.
Not sure how it works now - but way back when, the shop paid to send us to classes and it meant time out of the shop - meaning short staff in the shop. Small shops can hardly afford to lose even one person for a day, especially since some are still short-staffed from a couple of years ago. The dealership I have been buying from, the service manager actually joked with me that he had an open bay and " I have an open bay, I should bring you in since you know as much about these as anyone".
Sad state of affairs.

At least they had people who knew these things pretty well when it came time for the transmission replacement - think of it - that's actually one of the most critical parts of the 4xe - it's the main drive motor, connection between gas and electric drives, and a complex transmission in itself even without it being a 4xe - you have to know how to fill them properly, check fluid levels at just the right temperature, shut down the HV system and more.
Yeah, I can see how many shops out there aren't ready to work on these.
Heck, many don't understand the standard gasser electric system - when a tech tells me my winch was draining my batteries, and moves the winch ground cable from the top of the IBS on the battery negative to the chassis ground post as the FIX, when they are electrically the same thing........... what's that say? Especially when there was a big red switch set to OFF sitting right next to the battery, with the power cable going from the switch to the winch.
Seriously, the guy probably had trouble making a flashlight work.