Charging and Jump starting of Jeep JL Wrangler Batteries

MCJA

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Roy, I say this with a smirk I bet you and others can relate to. Much as I wish that first line customer service people knew answers like NASA ground specialists....

In work it's been my experience that the guy (or gal) with the true expertise is some subject matter...

...the one who knows the answer to your question before you ask it

..the one who corrects the form of your question to perfection--because they're pedantic

...the one who sighs because he/she gets this question so frequently and thinks people with merely average intelligence are idiots

...but yet the one you come to with trepidation because your other smiling fellow workers don't know "ship from shinola" the answer to your question.....but's are great with people

...don't often make great customer service reps. :):):)
Amen, amen, and amen.

"I bring the requirement from the customer to the engineer! I HAVE PEOPLE SKILLS!!"
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Thought I would add to this thread. Last night I left my KC HiLites on all night. Dumb, yes. As expected, dead dead dead this morning. Had to actually use my key to open the drivers door. So like a good faithful JL forum member, i looked for jump starting advice here instead of my manual. I got overwhelmed by ESS, double batteries, relays etc etc. Bottom line , I got out my trusty jumper cables. Hooked ip to my gf blue Honda Civic Hatchback. Connected to my battery positive terminal the old fashion way. Hooked the negative to the big metal knob just behind the alternator and as I read, let it sit for 7 min running before trying it. ( 7 minutes is mot listed specifically , just that with the two batteries it was best to let them charge a while before attempting a start) worked perfectly, just like any other jump start. Had my trickle charger all ready to go but just running for ten min in my drive while typing this I am already at 14.1 V. Started at 13.2 I think. So yes, dead as a door nail and jumped just fine.
 
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Thought I would add to this thread. Last night I left my KC HiLites on all night. Dumb, yes. As expected, dead dead dead this morning. Had to actually use my key to open the drivers door. So like a good faithful JL forum member, i looked for jump starting advice here instead of my manual. I got overwhelmed by ESS, double batteries, relays etc etc. Bottom line , I got out my trusty jumper cables. Hooked ip to my gf blue Honda Civic Hatchback. Connected to my battery positive terminal the old fashion way. Hooked the negative to the big metal knob just behind the alternator and as I read, let it sit for 7 min running before trying it. ( 7 minutes is mot listed specifically , just that with the two batteries it was best to let them charge a while before attempting a start) worked perfectly, just like any other jump start. Had my trickle charger all ready to go but just running for ten min in my drive while typing this I am already at 14.1 V. Started at 13.2 I think. So yes, dead as a door nail and jumped just fine.
Make sure you measure voltage with engine off. When it's on you are seeing the voltage the alternator is putting into your main battery.
 

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Not sure I'm talented enough to do that. I will say this. I was worried after I jumped and let it run for a while that I would restart. It restarted fine and all day long I start and stipped at least 6 times and the ESS worked perfectly each time I drove it. My only worry now is that the battery ( batteries ?) took a hit when they died. Not like boat batteries which are made to handle a lot of big discharged. I may get new batterries since it gets cold here and I go north now and then and hate the ifea of starting issues.
 

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Make sure you measure voltage with engine off. When it's on you are seeing the voltage the alternator is putting into your main battery.
Bobby, if I may, I'd like to also add that you may want to temporarily disconnect all wires leading to the negative side of the main battery before and during such a test, reconnecting them thereafter.

Not doing so will show what both batteries in parallel are providing, which by definition (when batteries are connected in parallel as they are in the 3.6L when it's at rest) doesn't change voltage just amperage.

After such a disconnection, testing the prongs of the main battery gives you its stats, while moving the tested negative side over to the disconnected negative wires gives you stats on the ESS/Aux battery.

Again--this applies to the 3.6L JL. And it's hardly an exhaustive test as the alternator, and both batteries' ability to give up and receive good charge need also be confirmed.
 

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Not sure I'm talented enough to do that. I will say this. I was worried after I jumped and let it run for a while that I would restart. It restarted fine and all day long I start and stipped at least 6 times and the ESS worked perfectly each time I drove it. My only worry now is that the battery ( batteries ?) took a hit when they died. Not like boat batteries which are made to handle a lot of big discharged. I may get new batterries since it gets cold here and I go north now and then and hate the ifea of starting issues.
That is one fast recovery sir. Just for curiosity Mark did you order your (3.6L) JL with the heavy duty alternator? It comes with the tow package?
 
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jeepdabest

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Bobby, if I may, I'd like to also add that you may want to temporarily disconnect all wires leading to the negative side of the main battery before and during such a test, reconnecting them thereafter.

Not doing so will show what both batteries in parallel are providing, which by definition (when batteries are connected in parallel as they are in the 3.6L when it's at rest) doesn't change voltage just amperage.

After such a disconnection, testing the prongs of the main battery gives you its stats, while moving the tested negative side over to the disconnected negative wires gives you stats on the ESS/Aux battery.

Again--this applies to the 3.6L JL. And it's hardly an exhaustive test as the alternator, and both batteries' ability to give up and receive good charge need also be confirmed.
I remove the aux negative cable from the post and test that way. Is that ok?
 

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I remove the aux negative cable from the post and test that way. Is that ok?
I'm sorry Bobby but to my way of thinking there's too many battery posts (4 in total) on the 2 batteries in your reference above and I want us on the same page.

So here goes. I'm going to stipulate everything from your question so we have 0 ambiguity....

Your ESS/Aux battery is tucked away below the Power Distribution Center (PDC): that black box just beyond the fire wall on the passenger's side and closest to the sky.

Getting to it is a pain.

But you can get to cables that lead to the ESS/Aux battery by either opening the PDC or easier, accessing cables that lead to the ESS/Aux battery that themselves normally connect to the posts on the main battery.

That said, on the main battery's negative post, using a wrench, loosen the bundle of black wires that ultimately connect to that post and separate them from the post, letting them dangle in mid air. Nothing should be on the main battery's negative post now.

Doing so will break the parallel connection between the two batteries (on the 3.6L JL at least) and allow you to test each battery independently.

With these cables detached, placing your tester prongs on the main battery's posts (the postive one with lost of cables attached to it and the negative one which currently has nothing on it) will give you statistics on the main battery only.

Moving the negative testing prongs off the main battery's negative post, and touching these negative prongs to the dangling and loose black cables will now give you stats on the ESS/Aux battery only. You can and should keep the testing prongs of the positive side on the main battery's postive post. Don't worry. You are not testing the main battery but the ESS/Aux one because cables on the postive post of the main battery that remain connected LEAD to the ESS/Aux battery, and you've competed the electrical circuit to the ESS/Aux battery only by touching the dangling wires we made loose prior.

Make sure to reconnect that black series of cable back on to the main battery's negative post after your testing and tighten the nut after your done with this testing.

With things put back the way you found them, and tests on the main battery's terminals will now---with all cables connected, test the combined amperage of both batteries....not what we wanted...hence the step to disconnect the negative wires above and in so doing isolate each battery electrically.

I hope this helps. : - )

Brandon Halon did a great job showing some of this in his video: He also has videos on testing things like the alternator:

 

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I do not have the towing package so I assume standard duty alternator. I bought used and at the time I did not realize all the extra items that came with the tow package.
 

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That was a great explanation on how to test, and actually seems easy. Is this test to tell the health of each battery? What should each read if healthy?
 

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That was a great explanation on how to test, and actually seems easy. Is this test to tell the health of each battery? What should each read if healthy?
Mark...I don't want to be one of those picky pains in the asses, but I'm going to be to make a point.

This test is to simply test each battery's current state of voltage and amperage at the time the test is made. We'd like to see voltages, I believe, above the 12V range on each battery.

Equally important, lets appreciate what this hardly exhaustive test doesn't do.

  • It doesn't test the ability for the batteries to deliver and receive charge--and the speed with which each does so as a reflection of battery health.
  • It doesn't test the alternator's abilty to deliver said charge.

What these basic test described above do effect are a basic look into whether the batteries have and hold charge. If they don't, service with more sophisticated diagnostic tools and tests are indicated, presumably by the dealer.

If they do though hold charge, such service by the dealer may still be indicated if your rig has issues with cranking and power.

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Thanks for this Bobby. While I made it only about half way through, the video's publisher's testing was very thorough and I think had a common thread through it as follows:

Despite these power packs often having features that allow for small power draw over longer periods of time, like a flashlight or USB port, their design--and it makes sense--is skewed towards delivering rapid strong charge in small periods of time, consistent with the large, but short in duration power needs of an internal combustion engine (ICE) to crank--or should I say its starter's need to overcome the forces of inertia and crank the engine.

This is much like how an electric motor often pulls more power proximate to being turned on, than that requried once it's achieved its operating speed.

And for most vehicles, but not the 3.6L Wrangler JL and its "by the manual" method of jump starting after hooking up the cables and waiting for a few minutes before attempting an engine crank, this makes sense.

The "problem" is that jump starting a 3.6L is a process of first charging both batteries during this waiting period, followed by attempting a crank. This pre-charging need can deplete a power pack of considerable charge when it may barely have enough juice to crank an engine mere seconds after being hooked up to a conventional ICE system requiring no pre-charging period, like most ICE vehicles.

Much has been written on this pre-crank waiting/charging period on the forum that I'd rather not rehash in totality, but feel it necessary to skim in explanation. What's going on in the charging period is that you're charging both batteries--which testing has shown are both used to supply power at crank time. But underlying this---the essence--is that you're really charging the ESS/Aux battery: which is connected to the main battery in parallel when the vehicle is at rest (and most other times as well except for a pre-crank test discussed below, and ESS events.)

You see, your 3.6L is going to test that ESS/Aux battery all on its own to see that it has a basic level of charge before even attempting a crank--much as the crank--as stated, is powered by both batteries. In fact, you could crank and operate your 3.6L on a decently charged ESS/Aux battery alone but you cannot crank it on the main battery alone as the pre-crank test of the ESS/Aux battery would fail.

If this pre-crank test of the ESS/Aux battery fails, the vehicle won't even attempt to crank the engine.

So--taking this out of the theoretical and into the real world, say your stranded in the middle of nowhere with one of these power packs that on its best day is of questionably adequate charge to crank your rig, and whose success may largely fall on just how dead your vehicle's batteries are. Your play here is to hook the power pack directly up to the ESS/Aux battery in parallel and attempt a crank as soon after this as possible, temporarily leaving the main battery out of the picture.

Method for doing this, in a way least likely to blow fuses, has been suggested here. https://www.jlwranglerforums.com/fo...-any-jumpstart-tips.12316/page-11#post-985376

In brief it involves temporarily disconnecting all the cables from the main battery's negative post so as to temporarily "take it out of the equation," hooking your power pack's positive end up to the positive post of the main battery and its negative end up to these dangling wires. Additionally a fused wire is connected between two fuses (N1 and N2) in the Power Distribution Center (PDC) so that the ESS/Aux battery isn't temporarily isolated from the power pack during the pre-crank test.
 
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