Jumperless Aux Battery Bypass

[Egress555]

I have a 23 Sport S, the main reason for me doing the bypass is because of using a dash cam 24/7 with parking mode. Noticed that my hardwired dash cam would shut off after my battery got voltage got low, as I know this is a feature built into most hardwired kits. So next thing I did was to purchase a AGM battery, went with a EverStart H7 after reading reviews here. I took out fuse 42 which was labeled the ESS fuse, then disconnected the negative wire for the auxiliary battery.

Now a couple weeks go by and I noticed my ESS started working. Any idea how this could happen?

Sponsored

 

[Mguy]

. . . . I took out fuse 42 which was labeled the ESS fuse, then disconnected the negative wire for the auxiliary battery.

Now a couple weeks go by and I noticed my ESS started working. Any idea how this could happen?

The speculative answer to your situation is that it took a while for the Jeep's computer brain to figure out the negative/F42 disconnect and your new main battery, so its now allowing ESS to operate. If that's correct, it's an overall positive for your Jeep, congratulation. Here's a further explanation.

The excellent post #1 in this thread should be understood to be the start of Course 102 for understanding the JL dual battery electrical system. Post #615 essentially ends the course.

 

[Jebiruph]

The speculative answer to your situation is that it took a while for the Jeep's computer brain to figure out the negative/F42 disconnect and your new main battery, so its now allowing ESS to operate. If that's correct, it's an overall positive for your Jeep, congratulation. Here's a further explanation.

The excellent post #1 in this thread should be understood to be the start of Course 102 for understanding the JL dual battery electrical system. Post #615 essentially ends the course.

But if this forum has Course 101, I don't know where it begins and where it ends. There are too many threads, too many posts, and too much sloppy reference and description (including by Jeep itself) to "ESS" and the smaller aux battery without differentiating the two. So, to simplify . . . .

The dual battery system is inherently flawed, resulting in the short life of both batteries for many, if not most, owners. The primary cause is that the batteries are dissimilar, resulting in charging complexity which doesn't usually work well. The problem is harder to solve because of the finicky charging preferences of the otherwise desirable AGM type lead batteries. Even external charging has issues, and is inconvenient for most owners. Finally, allowing ESS to operate aggravates the situation because it stops all charging (by shutting the engine) while loads are kept on.

A quick and easy mod, the aux battery negative/F42 disconnect, converts the entire electrical system to a better performing, easier to charge, single battery setup. However, the mod still permits ESS to operate. Shutting off ESS (manually on the dash or with aftermarket hardware and software) will significantly improve overall electrical performance for most (if not all) owners by preventing engine shut off and charge stopping.

Try here for 101 https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/

 

[Mguy]

Try here for 101 https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/

In March, 2019, many new owners of the new JL were experiencing a slew of electrical problems that would swell 1960 era Jaguar owners with schadenfreude. The above thread was needed, and based upon information then available, obviously a very helpful resource. It deserved everyone's sole nomination for course 101

 

[Egress555]

Jebiruph, Mguy, Thanks guys definitely explains a lot.

 

[beewil]

The speculative answer to your situation is that it took a while for the Jeep's computer brain to figure out the negative/F42 disconnect and your new main battery, so its now allowing ESS to operate. If that's correct, it's an overall positive for your Jeep, congratulation. Here's a further explanation.

The excellent post #1 in this thread should be understood to be the start of Course 102 for understanding the JL dual battery electrical system. Post #615 essentially ends the course.

But if this forum has Course 101, I don't know where it begins and where it ends. There are too many threads, too many posts, and too much sloppy reference and description (including by Jeep itself) to "ESS" and the smaller aux battery without differentiating the two. So, to simplify . . . .

The dual battery system is inherently flawed, resulting in the short life of both batteries for many, if not most, owners. The primary cause is that the batteries are dissimilar, resulting in charging complexity which doesn't usually work well. The problem is harder to solve because of the finicky charging preferences of the otherwise desirable AGM type lead batteries. Even external charging has issues, and is inconvenient for most owners. Finally, allowing ESS to operate aggravates the situation because it stops all charging (by shutting the engine) while loads are kept on.

A quick and easy mod, the aux battery negative/F42 disconnect, converts the entire electrical system to a better performing, easier to charge, single battery setup. However, the mod still permits ESS to operate. Shutting off ESS (manually on the dash or with aftermarket hardware and software) will significantly improve overall electrical performance for most (if not all) owners by preventing engine shut off and charge stopping.

Thank you for the information. I have ordered a 2024 Unlimited JL Rubicon X. Would you advise the Auxiliary battery negative/F42 disconnect within the first day or two of me owning the jeep? they have made some tweaks to this jeep and I’m just wondering if everything‘s the same for the batteries and electrical as previous models?

I plan on getting a SS turn off switch as well like the tazer mini. All it does is remember what setting the start stop was on when you turn the jeep off. So if the SS was off when you turned the jeep off, it would keep it off when you restart the jeep. I guess I would just have to be aware that if I take the jeep in for warranty work, I’d have to reinstall F 42 and negative disconnect and remove start/stop bypass switch under the dash?

I guess I would, eventually, after the 3year warranty expires, remove the auxiliary battery?

or would you suggest just leaving the system alone and getting a battery tender system/trickle/maintenance which will charge/maintain both batteries?
Thanks.

 

[Heimkehr]

I plan on getting a SS turn off switch as well like the tazer mini.

So if the SS was off when you turned the jeep off, it would keep it off when you restart the jeep. I guess I would just have to be aware that if I take the jeep in for warranty work,...

The one time my JLU saw the dealer for a potential warranty issue (wonky O2 sensor), I left the ESS defeat harness in situ. By necessity, it's well out of sight under the dashboard.

Prior to turning over the fob, I reactivated the function via a button press on the dashboard and that was that. The Svc Dept. didn't mention anything, so it's possible that they took no notice here.

Just one example.

 

[Mguy]

I have ordered a 2024 Unlimited JL Rubicon X. . . .

Congratulations on your order, may the wait time pass quickly. First, you mention possible new improvements that might affect the dual battery system. If there is dual charging that's something, but otherwise I'm skeptical.

New JL owners are going to fit somewhere among a widely varied group. Alaska to Florida, tundra to the beaches. Drivers with ESS stops and only one hour charging time daily. Overlanders with a month or more between long trips. Every owner has a different risk tolerance for mods and warranty work, and a different dealer pain threshold. It all goes in the mix. So I can't say what I would do if I were you. I'd make a lousy advice columnist.

But I can say what I'd do if I were in the market for an off road capable vehicle. I'd buy a manual transmission Rubicon because I really like, and need, my "old" Rubicon a lot. The dual battery system on a new Rubicon would not slow me down at all.

After taking delivery I'd make sure the dual battery setup was as with my "old" Rubicon when stock, assess again the options for dealing with it's flaws, and then undoubtedly decide to do the negative/F42 disconnect again. No reason to wait once the decision is made. After the mod I would verify/charge both batteries to 100% capacities. Then it's 30 days of care free use and enjoyment before another option reassessment and verify/charge. Future use and enjoyment periods would be about 90 days.

ESS on my "old" Rubicon, modified with the negative/F42 disconnect, is manually shut down after each start, but once in a while left on to take advantage of it's general diagnostic property. It did predict and help find a bad temperature sensor, twice.

Good luck, and tell us about your experience with the newest version Rubicon, and whether Jeep has solved any dual battery issues.

 

[rogers]

I did the bypass while the Aux battery was still functional. I keep my Aux available for emergency use or for if/when I may need to to add it back to the system. Even though it isn't being used for anything I put the trickle charger on it every 3 weeks and it does take a couple of hours or more to recharge 100%. So it does discharge slowly while in this state of disconnect.

Hi, I know this post is older, but how do you get to the positive part of the AUX battery to charge it?

 

[Rhinebeck01]

Hi, I know this post is older, but how do you get to the positive part of the AUX battery to charge it?

@rogers

When you want to maintain/charge just your Aux battery, you hook up the positive clamp on your battery charger/maintainer to the positive terminal of your Main battery. You take the negative clamp of the battery maintainer / charger and hook that up to the Aux battery negative cable that you have disconnected from the Main battery negative terminal..

 

[rogers]

@rogers

When you want to maintain/charge just your Aux battery, you hook up the positive clamp on your battery charger/maintainer to the positive terminal of your Main battery. You take the negative clamp of the battery maintainer / charger and hook that up to the Aux battery negative cable that you have disconnected from the Main battery negative terminal..

Ah, thanks a lot. That's easy. ?

 

[Leisure Freak]

Hi, I know this post is older, but how do you get to the positive part of the AUX battery to charge it?

The Aux bat is still connected at the main bat Pos terminal. The aux bat is isolated because it no longer is connected to ground. I cut off a piece of bike inner-tube to attach with zip tie to the disconnected aux neg cable end to protect it from hitting ground and be able to peel it back like a foreskin to get to it for charging. I connect the charger directly on the main pos terminal and the neg/ground on the disconnected aux bat cable end.

 

[Grayone]

Anybody have a 2024 with factory winch that has disconnected negative aux cable? If so got a photo of which cable is neg to aux? Don't want to mess up and disconnect wrong one. Thanks.

 

[rogers]

The Aux bat is still connected at the main bat Pos terminal. The aux bat is isolated because it no longer is connected to ground. I cut off a piece of bike inner-tube to attach with zip tie to the disconnected aux neg cable end to protect it from hitting ground and be able to peel it back like a foreskin to get to it for charging. I connect the charger directly on the main pos terminal and the neg/ground on the disconnected aux bat cable end.

That's how I did it, but I wasn't sure if it would really work.

Sponsored