DIY How-to: Take the Aux Battery Offline

[Lunentucker]

Baffling to me how so many continue to try to defend this inherently flawed design. It's very well-documented and it's not normal for modern vehicles.
At the very least they should have made the consumable part, AUX battery, more accessible. Batteries do not last forever. Burying one way down low, out of the engine compartment, and exposed to the elements and water is just plain careless for a supposedly "capable off-road vehicle".

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[sharpsicle]

Baffling to me how so many continue to try to defend this inherently flawed design. It's very well-documented and it's not normal for modern vehicles.
At the very least they should have made the consumable part, AUX battery, more accessible. Batteries do not last forever. Burying one way down low, out of the engine compartment, and exposed to the elements and water is just plain careless for a supposedly "capable off-road vehicle".

Not defending the battery choices or the location. Just pointing out that there are factually incorrect things being stated. Baffling to me how many can't separate the two and understand the difference.

Why is everyone so tied to the notion that ESS is the root of every problem when it isn't? It might be annoying, sure, but it's not killing your Jeep.

 

[DNNDRTY]

I can show pictures of a Jeep being jump started. That's about as useful as a picture of one on a tow truck.

This is asinine. Remove your aux if you want. Nobody cares. Demand that NHTSA opens an investigation. They won't. Find echo chambers that parrot the same bad information over and over. Won't change the true problem: it's the crap factory batteries, not the ESS system, that are the problem.

I’ve run both yellow top optima and odyssey battery and experienced this issue. Not sure what else to share or tell you outside of pictures and my experience. I can try to do a video if it happens again, but I am sure someone will object still.

Those who experience know what I am talking about with this flawed design. In no way should the aux battery cause a vehicle not to start or stop a vehicle when the main battery is good (or was good until the aux battery drained it because of bad design)

 

[DNNDRTY]

Not defending the battery choices or the location. Just pointing out that there are factually incorrect things being stated. Baffling to me how many can't separate the two and understand the difference.

Why is everyone so tied to the notion that ESS is the root of every problem when it isn't? It might be annoying, sure, but it's not killing your Jeep.

I don’t have qualms with ESS. If aux battery is bad, ESS should just not work (just be shutoff) vs what is currently configured with aux battery being bad it prevents Jeep start and starts draining main battery.

Next round I will bypass or go genysis dual battery route.

 

[RIPLER]

What's your voltage? Your main is probably close to dead too.

I just measured it and it's about shot, measured 12.4V. I'm going to go get a new main battery after work and keep this mod in place. I'm just confused as to why I didn't get the auxiliary switch message until I did the mod.

 

[Mr._Bill]

I just measured it and it's about shot, measured 12.4V. I'm going to go get a new main battery after work and keep this mod in place. I'm just confused as to why I didn't get the auxiliary switch message until I did the mod.

The two batteries are paralleled together all the time, except during the initial startup test of the Aux Battery. You removed a good Aux battery which was masking the condition of the failing Main Battery. Once the Aux Battery was gone, the Main Battery was left to handle things on its own and the true state of the battery became apparent.

 

[Dryfly24]

I have a 2020 with 40k miles. Main battery changed last year.

As @ShadowsPapa says, These things always get so convoluted it’s hard to follow exactly what is and isn’t and it’s frustrating for some of us who aren’t as mechanically savvy. I can work a wench ok but I do t know $chit about electrical issues/systems and don’t always understand all the acronyms. So it gets very frustrating.

This is all I want to know, please just focus on these questions so I do not get bogged down with a bunch of other info I don’t need.

1) If I do this mod and leave the aux battery in, will it be completely isolated from the system and not do anything. Essentially just sit there taking up space and adding weight, or will it still contribute power to the system?

2) People keep talking about how the aux battery can drain the main then also prevent you from jumping the truck conventionally. Some say this isn’t true, others say it is. Which is it?

3) When my main battery went last year, I couldn’t jump it. I went and replaced the battery and all was fine. it happened in my driveway so no harm no foul.
I’m just afraid of going Offroad to the middle of nowhere and getting stranded in the desert without being able to simply jump my truck again. I’m starting to get the messages again and my start/stop system hasn’t worked for a long time. Is the aux battery bad thereby killing my main? Or is it more likely/probable that the main is bad?

I bought the biggest, baddest, bestest battery O’Reilly’s had. Kind of hard to believe it’s already dying unless something is seriously draining it.

 

[Lunentucker]

I have a 2020 with 40k miles. Main battery changed last year.

As @ShadowsPapa says, These things always get so convoluted it’s hard to follow exactly what is and isn’t and it’s frustrating for some of us who aren’t as mechanically savvy. I can work a wench ok but I just don’t always understand all the acronyms. So it gets very frustrating.

This is all I want to know, please just focus on these questions so I do not get bogged down with a bunch of other info I don’t need.

1) If I do this mod and leave the aux battery in, will it be completely isolated from the system and not do anything. Essentially just sit there taking up space and adding weight, or will it still contribute power to the system?

2) People keep talking about how the aux battery can drain the main then also prevent you from jumping the truck conventionally. Some say this isn’t true, others say it is. Which is it?

3) When my main battery went last year, I couldn’t jump it. I went and replaced the battery and all was fine. it happened in my driveway so no harm no foul.
I’m just afraid of going Offroad to the middle of nowhere and getting stranded in the desert without being able to simply jump my truck again. I’m starting to get the messages again and my start/stop system hasn’t worked for a long time. Is the aux battery bad thereby killing my main? Or is it more likely/probable that the main is bad?

I bought the biggest, baddest, bestest battery O’Reilly’s had. Kind of hard to believe it’s already dying unless something is seriously draining it.

1. Without being grounded the battery can't be a battery, dead or alive.
2. I have seen numerous first hand real world accounts of that happening. I trust that under the right circumstances it can occur. Why take the chance when you don't have to?
3. There's no way to know for sure until they are separated, charged and tested separately. The great flaws in this setup are that
A - One battery can take the other one down with it, and you won't know until it's likely too late.
B - The electronics do not monitor both batteries independently.
C - Access to a consumable like the AUX battery should be vastly better. There are two ways of getting to the battery, which absolutely positively without a doubt WILL need to replaced at some point, and neither of them are Advance Auto parking lot easy.

The only thing you really lose from taking the AUX battery out of the picture is the increased risk of failure. Millions of cars on the road with one battery and advanced electronics.

 

[LouisvEarlleJT]

Just going to throw this out there again for any lurkers.

mine battery CAN NOT “kill” the other battery with how they’re wired. A short in the wiring must be present for that to happen. Could be at the connections. Could be in the wire somewhere. A dead battery will not pull current off a live battery.

for a simple analogy: If you have a dead remote that holds two AA’s and you replace one dead AA with a fresh AA the remaining dead battery does not kill the new one. The main and aux battery are essentially wired up the same.

 

[LouisvEarlleJT]

I guess I should play the lottery. I must have good luck. My 2020 will be 4 years the end of august with the original batteries. I should also be looking at replacement. Does anybody recommend paying the xtra cash for brands like optima etc. I tried lithium in my Road King and lasted one year and it gave out and swelled so much it looked ready to pop. Thanks for any recommendations.

I don’t know if you’ve bought a battery yet but Duracell makes GREAT auto batteries. I’ve put them in everything for years. Got one that’s going on nearly 8-9 years old. They can be found at Batteries Plus stores and even come with a 5 yr warranty.

 

[ShadowsPapa]

mine battery CAN NOT “kill” the other battery with how they’re wired. A short in the wiring must be present for that to happen. Could be at the connections. Could be in the wire somewhere. A dead battery will not pull current off a live battery.
for a simple analogy: If you have a dead remote that holds two AA’s and you replace one dead AA with a fresh AA the remaining dead battery does not kill the new one. The main and aux battery are essentially wired up the same.

Sorry - incorrect. The batteries in your remote are SERIES. The batteries in the truck are PARALLEL.
If the main battery develops a short internally, then it becomes a load on the small battery and drains it.
IF the aux battery develops a short internally then it becomes a load on the main and kills it.
When in parallel, if one battery becomes a LOAD, then it's like placing a resistor across the terminals of the other battery, draining it
Can't happen in your remote with AAA or AA batteries because there is no complete circuit.
I was creating things in electronics before I even hit high school, including batteries, crystal radios, color organs, shoe box motors, etc.

1) If I do this mod and leave the aux battery in, will it be completely isolated from the system and not do anything. Essentially just sit there taking up space and adding weight, or will it still contribute power to the system?

2) People keep talking about how the aux battery can drain the main then also prevent you from jumping the truck conventionally. Some say this isn’t true, others say it is. Which is it?

3) When my main battery went last year, I couldn’t jump it. I went and replaced the battery and all was fine. it happened in my driveway so no harm no foul.
I’m just afraid of going Offroad to the middle of nowhere and getting stranded in the desert without being able to simply jump my truck again. I’m starting to get the messages again and my start/stop system hasn’t worked for a long time. Is the aux battery bad thereby killing my main? Or is it more likely/probable that the main is bad?

1. IF you do the mod and remove the aux battery ground cable from the IBS then it's isolated. BOTH aux battery cables must be connected for it to be in a circuit. It's like both wires of a resistor must be connected for it to be in a circuit, and both terminals of a light bulb must be connected for it to work.

2. People keep repeating stuff they read even if it's wrong - and the more time it gets repeated, then the internet takes it as fact. Copy and past things often enough, people see it all over and assume it's true. That's the sad part of the internet. IF someone sees something repeated often enough without being countered by facts from people with training and experiences, then it's fact and once a person who knows the truth tries to counter it, it won't be believed because of the number of times the BS is repeated.
FACT - either battery could be the first to go - could be the aux, but could be the main, and which goes first depends on a whole list of things. So could be aux, could be main
FACT - a battery can go bad and NOT impact the other battery! A cell can go bad in such a way that it's not shorted, but more open, or in other ways. That battery will not carry a load but also will NOT drain the other battery. So if one goes bad - will it kill the other? There's a chance, but not a big chance. It's just that when it does happen, those people jump on the internet and yell loudly about it warning others that this WILL happen because it happened to them. However, I've had it happen the other way, too.

3. Sometimes jumping doesn't work because a very dead battery is like a huge load, acting almost like a "short" on the battery doing the jumping on the live vehicle. People connect the cables, jump in and oops, it won't start. You should never do that. You should always give a a while to attempt to build up the dead battery. Some jump packs just can't handle that.
Connect the cables, wait a while, then attempt the start, otherwise all of the power is going into the dead battery. Frankly, this can happen anyway and those of us who have been in the business for decades have run into this in non-Jeeps years ago.
The donor vehicle that is running must overcome the load of the dead car's battery PLUS furnish enough to power the ignition and starter of the dead vehicle. Again, some jump packs don't do well with this.

A few weeks ago someone posted a good youtube video of a fellow comparing jump packs and it was interesting which ones didn't do as well as some of the others. Some owners of a certain brand may wish to reconsider and buy a better one next time........ I think it was a Project Farm video - some of their videos just aren't good comparisons and their tests leave a bit to be desired but their testing of the jump packs left little to pick apart - it was pretty good.

In short:
1. Disconnect and isolate that aux battery ground and there's just no way it can do anything but sit there.

2. It can happen, it can be either way. It's magnified by the internet. Look at the polls here - yeah, it's happened - but is the risk high? No. People on the internet make really sure they get attention when it happens, though, making it look worse. The chances of it happening aren't great. These systems have been used by BMW, GM and others - it's not a "jeep thing". Only the battery placement is a jeep thing. Jeep did not invent this system.
My wife's 2018 Grand Cherokee lost the batteries - I was able to EASILY jump start it with a jump pack and BOTH batteries were bad!

The only way to know about the final health of your batteries is to independently fully chare each - charge the aux battery and test it (LOAD TEST IT BY A PRO, NOT A PARTS STORE!)
independently charge the main battery and load test it - again, by a pro, not a parts store counter guy who doesn't know more than what he reads.
Once you get to 2.5 - 3 years on original Jeep batteries, consider replacing them soon. If they don't test great, replace them if you will be in the wilderness.

I have been doing auto electric since I was 14 - yeah, that's right, 14, that would have been in 1971. Got a job in an auto repair shop (a former AMC dealership) at 16. Specialized in the electric systems (charging/battery, ignition, etc.) in the Plymouth troubleshooting contest in 1975 - set records, first place. Degree in automotive - As in the electric systems classes (eventually dean's list)
First job out of college in an auto shop I got by diagnosing ignition issues on a Ford using the Sun scope - the service manager was having trouble and told me if I could tell him what was wrong, I'd have the job. 5 minutes later I had the job.
Cold call from manager of Bud MulCahy Jeep/Eagle offering me the job of service manager - which I turned down. i enjoyed my then current job too much where the boss gave me a lot of free reign and I loved the customers.
Fast forward to today - I restore automotive electric systems on classic cars, put a Jeep engine and electronics in my car and won gold, along with best of show, 2018.

So, sorry, but I cringe at half the crap I see on the internet, especially from people who have experience with one time on one vehicle in the last few years - and see results or symptoms but don't understand the underlying causes, so they make up something that fits.
People hate not knowing causes - so way too often, make up something that seems to fit, and the internet buys it because it gets repeated by others that don't understand.

In the end - it's your Jeep. Do what you want, what you feel comfortable with.
You won't harm anything - but know that if you leave it that way and take it in for warranty work on electrical, they may balk. But this is none-invasive so could be put back really quick before that visit. They have the right to not grant warranty on modified electric systems. In this case put the cable back, put the fuse back.

 

[ShadowsPapa]

Just going to throw this out there again for any lurkers.

mine battery CAN NOT “kill” the other battery with how they’re wired. A short in the wiring must be present for that to happen. Could be at the connections. Could be in the wire somewhere. A dead battery will not pull current off a live battery.

for a simple analogy: If you have a dead remote that holds two AA’s and you replace one dead AA with a fresh AA the remaining dead battery does not kill the new one. The main and aux battery are essentially wired up the same.

For the lurkers - this is very incorrect.
Our Jeep batteries are in parallel.
Your remote batteries are in series.
Our Jeep batteries are always connected together except during a brief moment when starting or during an ESS event..
Your remote batteries are not connected electrically as you have not pressed a button so there is no complete circuit.

In parallel, if the battery on the right has a "short" or debris has sloughed off and settled completing a circuit from + to - then it will drain the battery on the left.
If EITHER one shorts or the resistance drops dramatically, usually through age, mis-use, deep cycling, etc. then it becomes a load directly across the terminals of the other battery.
These are in parallel - (our batteries are in parallel when sitting and the engine is running)
It's NOT common, but can happen. And it can happen EITHER WAY. main can fail draining the aux, or the aux can short and drain the main. If this is caught and the bad battery replaced, it won't necessarily ruin the other battery, just drain it. It's still possible it's ok. Draining a battery one time doesn't ruin it - but it does drop capacity and shorten life. This is why some Jeep owners have replaced ONE of the batteries and moved on. It all depends on the depth of drain, speed of the drain. It's like leaving the headlights on on an older vehicle - it DRAINS the battery but doesn't necessarily ruin it. Draining a battery one time will not necessarily ruin the battery - it does it no good, of course.

in series that's not possible as there's no complete circuit across the terminals of either of the batteries through the other battery -

Follow the yellow/orange path and note that the positives are connected together through the PCR and high current fuse.
The negatives are tied together directly -

 

[Dryfly24]

1. Without being grounded the battery can't be a battery, dead or alive.
2. I have seen numerous first hand real world accounts of that happening. I trust that under the right circumstances it can occur. Why take the chance when you don't have to?
3. There's no way to know for sure until they are separated, charged and tested separately. The great flaws in this setup are that
A - One battery can take the other one down with it, and you won't know until it's likely too late.
B - The electronics do not monitor both batteries independently.
C - Access to a consumable like the AUX battery should be vastly better. There are two ways of getting to the battery, which absolutely positively without a doubt WILL need to replaced at some point, and neither of them are Advance Auto parking lot easy.

The only thing you really lose from taking the AUX battery out of the picture is the increased risk of failure. Millions of cars on the road with one battery and advanced electronics.

Exactly the answers I was looking for thank you! ????

 

[LouisvEarlleJT]

…

Holy cow mate, it was a bad analogy about a remote. No need to quote it twice lol. My point was to counteract the screaming voices saying that the system is flawed and that a dead aux WILL kill the main. Something you’ve said many times on here.

I.e. we agree, I think.

 

[ShadowsPapa]

Exactly the answers I was looking for thank you! ????

If I were to do this mod - I'd right away opt to replace the main battery with the biggest battery that will fit that tray, and the highest Ah available in that size.
You will be running everything from that one battery, so the "millions of ...... are operating on one battery" while true, is not the whole story - they will have a larger "one battery" because now, everything is depending on that one battery. And if you have after-market parts installed like lighting and other fun stuff - the charging system may not keep up at idle so you need the batter as a backup.

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