Jumperless Aux Battery Bypass

[Chubrocker]

Big thank you to OP and everyone else. Have a 2018 with no tsb and it was a complete no start. Followed instructions and works great. Bought a new main (larger h7) for peace of mind when wheeling and that fit well. Have a tazer mini and stop start is always off.

Battery rug thing didn’t fit. Cut 2 slits on the short side and it covers pretty decent.

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[TimR]

14.4 "almost all the time" is not at all typical.. it is not what you want to see or should see.

As for the earlier post that says "drop to around 12.5v while driving"., well that is not at all typical either.

Then what is typical?

 

[Rhinebeck01]

Then what is typical?

@TimR

For sure not 14.2 or 14.4 all the time while you are driving...

Yes, 14+ when you first start driving after the JL has been sitting for a day or whatever, but as you drive you should see it drop down to say 13.2, 13.4, 13.6. , 13.8... As you drive you will see it go up and down..... but again, not typical to see pinned all the time, at 14.2, 14.4.

As for 12.5, I have never seen my JL or any JL/JT be driving along with 12.5 ....

 

[TimR]

@TimR

For sure not 14.2 or 14.4 all the time while you are driving...

Yes, 14+ when you first start driving after the JL has been sitting for a day or whatever, but as you drive you should see it drop down to say 13.2, 13.4, 13.6. , 13.8... As you drive you will see it go up and down..... but again, not typical to see pinned all the time, at 14.2, 14.4.

As for 12.5, I have never seen my JL or any JL/JT be driving along with 12.5 ....

Good to know. Thanks!!

 

[Wrangler man]

So, no errors, Aux battery is bypassed and ESS is disabled? If so, this is absolutely awesome

Or does ESS function as it would with the N1/N2 jumper...

The ESS Is now completely disabled. We pulled And taped offthe negative cable from the auxiliary battery and pulled the fuse. 0 issues perfect easy free fix. The final test will be whenThe battery dies will my jumper Box be able to start the dead battery now that the auxiliary battery has been disabled. Everything I've read and studied it will work as any other automobile does either jumped by set of jumper cables from a secondary car or using my battery pack jumper Box

 

[Kleiss1]

Driving back to Phoenix from Mexico today my 2021 JLURD was show 14.5 running 75 with just radio on. No A/C or anything. Is this a sign the main is going bad? Thanks

 

[Jebiruph]

My sport is brand new. six months old.
voltage reads 14.4 almost all the time. Always has.
if I let ess stop the engine you see the voltage start dropping.
otherwise, 14.4 while engine is running.

While this is not typical, mine was 14.4-14.7 for around 2.5 years without any other issues or symptoms. What did my main battery in was a accidently leaving an accessory powered on when the JL was turned off. The aux battery still tested good when I replaced it after 3.5 years.

 

[eck]

Appreciate the writeup, I just did this on my '18. I replaced the main back in April, the aux still tested good so I've been running with it for the last 7 months. I usually keep the battery meter up on the dash and noticed the past couple of weeks the voltage has been sitting at 14.4V even after a good long trickle charge. Isolated the aux today and while it still tested good it's definitely on its way out.

I pulled the fuse and the aux negative and took it for a spin around the block to make sure everything still works. Now I've got the main on the charger and hopefully the smart charging sorts itself out, although I'm expecting it might take a week or so for the IBS to get used to the new setup.

 

[Jebiruph]

I pulled the fuse and the aux negative and took it for a spin around the block to make sure everything still works. Now I've got the main on the charger and hopefully the smart charging sorts itself out, although I'm expecting it might take a week or so for the IBS to get used to the new setup.

With a fully charged battery, a reset IBS should sync up in hours after an initial engine on, engine off cycle.

 

[eck]

With a fully charged battery, a reset IBS should sync up in hours after an initial engine on, engine off cycle.

I did a couple of short drives last night and then left it on the charger overnight. This morning it was mostly hanging around 13.7V. I feel much better now

 

[Oncorhynchus]

I’ve got a 2018 3.6 (thus should be the old configuration of the battery negative termonal connection) and my aftermarket main battery reads 12.8V on a voltmeter with all cables disconnected. But my battery reading on the dashboard shows 0.0V. (I’ve got the jumperless ESS configured right now).

Could it be a bad battery sensor?

Or do I need to run an OBD scan to clear an error code which may be preventing the Jeep from starting (and realizing the main battery is not dead).

 

[wheels082]

I have a 2018 and pulled the fuse and disconnected the negative cable to the auxiliary battery. All good so far. At some point, I think I would like to completely remove the aux battery. Are there any issues with removing it?

 

[PatrickR]

Hey all, pulled the fuse and the terminal and I still have the avengers symbol on the dash (ess error). I had the ess error before I pulled the fuse (which prompted my investigation into a bad aux battery - I had just replaced the main). Do I have to do something to clear the ess error?

 

[4x4tographer]

I have a mid-year 2018 3.6 and just performed this "mod" today. I have the TSB 18-092-19 update that was applied back when it first became available. The Aux battery has been a real landmine for me in the past and has led to a fair amount of heartburn as I use my Jeep in the AZ backcountry fairly often.

Bit of recent backstory -
I recently forgot to turn off my GMRS radio and left the Jeep sitting for about 8-9 days. I was able to start the Jeep, but it really had to pull deep to get it going.

I pulled the F42 fuse and then disconnected the Aux ground. Jeep tried to start, but failed - as expected. However, on the 2nd attempt it wouldn't turn over - Main battery was toast, reading 9.8v. When the Aux was previously connected it would at least grunt and turn over, so I'm assuming it was in parallel at the time and giving the main some guts to get her going.

Jumped the Jeep with F42/Aux still disconnected and used my NOCO for the boost.

Hit up Autozone today and installed a new Duralast Platinum AGM H7 Group 94R. Jeep fires right up. No errors or issues across about a dozen starts today.

I'll keep you guys posted if I run into any issues. I'm running the Bradshaw Trail this weekend in Southern California desert, so we'll be out in the cold for a few nights and using some accessories.


Massive thanks to @Jebiruph @Rhinebeck01 and everyone that has contributed to this thread and all of the other countless pages of battery knowledge on the forums. The Aux battery is truly an unwarranted PITA for all of us. If you're ever in North Phoenix, I'll buy you a beer!

 

[Fudster]

I have a 2018 and pulled the fuse and disconnected the negative cable to the auxiliary battery. All good so far. At some point, I think I would like to completely remove the aux battery. Are there any issues with removing it?

No. Pulling Fuse 42 makes all calls for power to whichever battery or batteries are available, both, just the Aux or just the main.

Fuse 42 prevents a normally closed relay that connects the two batteries, or whatever, if anything you have attached to those battery leads (including nothing on the Aux battery) from over opening and separating the batteries.

Do make sure ESS doesn't turn on though either by pressing the ESS off button or buying tech to turn it off for you, otherwise ESS events will be powered off the main battery whose powered will be taxed post ESS event and whose ability to crank then could be compromised.

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