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The ESS battery should have been bigger, much bigger?

AndySpill

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The intro

We can conjecture on the exact reasons for Stellantis' decision to incorporate two AGM batteries into builds of what I believe are the most common engine configurations of the JL. I've often theorized that the dual battery design protects the main battery, to bare the bulk of the cranking power after an ESS event, and that such designs might be more critical in vehicles like the Wrangler, historically subjected to larger numbers of owner modifications, particularly with electrical current drawing appliances: from stereo systems, to lights, to winches, to off roading/camping gear etc. that drain a battery during an ESS event, not subject to replenishment from an alternator that is as motionless itself as the engine it depends on, during such ESS events.

I recently read here that the dual battery decision was fueled, of all things, by problems in testing with the entertainment system's need for more stable voltage during ESS events.

And sure, the Bronco runs ESS with one battery as does "your father's Oldsmobile," but at least for the latter, aftermarket appliances are often limited to "smart phone charge cords:" not very demanding of electrical power.

And yes Stellantis could have designed a better ESS system (or maybe pushed their entertainment system subcontractor for better product) but we would have had to pay for that. Their goal, as I see it ,was to pass an EPA test, meet CAFE standards and not get hit with whopping penalties that we'd have to share with them in purchase cost.

People who like ESS can probably fit in a phone booth. Its gas savings likely wouldn't justify the out of pocket (if not environmental as well) cost of a better design that people don't want. In fact there appear to be two camps: those who tolerate ESS and those who really hate it. And even though ESS systems do in bulk save fuel, net net, are all the used up battery components that aren't recycled and buried in land fills not merely staving off CO2 output for ground contamination, not to mention the green footprint to manufacture those batteries in the first place? Are we not simply putting off one green problem (ground contamination) to address perhaps or more pressing one (too much CO2 in the atmosphere)?

And all this comes from a green centric forum member.

The question

With all this said, many of us agree that the ESS battery is too small, and that a better design, given that the batteries are connected in parallel, might involve identically sized batteries as Shane's done so well at @Genesis Offroad, even if those equally sized batteries aren't as big as the two sizes offered for main batteries from Stellantis in their dual AGM battery JL offerings. Maybe even better, allow the batteries to periodically change roles of being the main and ESS battery, which doesn't seem like a difficult or expensive design that a bistable relay couldn't address.

But maybe the ESS battery should have actually--and maybe this is purely academic--been bigger than the main battery.

Jeep Wrangler JL The ESS battery should have been bigger, much bigger? 1710956898283-ah


We tend to need lead acid batteries (of which AGM batteries are a variant, known for their faster ability to charge and discharge like ESS events need, over mere sealed lead acid batteries) unless you can limit your travels to warmer non-freezing climates suitable for LiFEPO4 battery offerings. And AGMs tend to last longer (in time/charge cycles, if not in total lifetime amps drawn) when their depth of discharge (DOD) is minimized.

So we have this tiny battery being pushed to even further DODs than the main battery, delivering power at some times that it isn't simultaneously being replenished by an alternator (ESS events) crapping out and taking the main battery with it. Meanwhile, barring the cranking process, our larger main battery enjoys delivering power under an environment that finds a smart alternator replenishing it (and yes the ESS battery too, which also supplies power in non ESS events) real time.

Maybe, even if not cost effective, an ESS battery larger than a main would find both lasting longer. Maybe not.

Flame away!

(@THAW I hope you will add your thoughts here despite our past differences, as my issue has not been with your otherwise strong battery acumen, but more my understanding you.)
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Reinen

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The Aux battery being small isn't as big a problem as most think. When it is isolated the electronics it powers doesn't have a large draw, but it does need to be clean power. Given that Jeep owners fully expect and do install a significant amount of electrical add-ons, this is clearly a concern and the reason for the dual batteries. Yes, one battery will work. Until the batteries age and it doesn't. Then everyone will blame the Jeep and not their electrical mods. (Engineers do think about what people will blame)

The question is why do people say you should have the same size batteries in parallel. Size is actually irrelevant. Resting voltage is what matters. You want the batteries to have the same resting voltage or the weaker battery will weaken the stronger battery until they are balanced, then it's a non-issue. The most likely way to have two batteries with the same resting voltage is for them to be the same size, same manufacturer, same age, same use. But it's not the only way.

That's the reason, it has nothing to do with battery size itself as power draw will balance between the two. It also goes to show that the worst possible thing you can do for battery longevity is mixing a new Main with old Aux or vice versa. They will have drastically different resting voltages regardless of their size or manufacturer.

I do have to say that the @Genesis Offroad Aux battery relocation kit that replaces both Main and Aux with two Group 25 batteries is a great option. Different size batteries is only a small problem but it is still a problem. While Aux doesn't NEED to be Group 25, it is better if it's the same size & manufacturer as the Main. It will also straighten out a lot of people's thinking if they can see Main & Aux side by side instead of Aux being a hidden mystery.
 
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AndySpill

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The Aux battery being small isn't as big a problem as most think. When it is isolated the electronics it powers doesn't have a large draw, but it does need to be clean power. Given that Jeep owners fully expect and do install a significant amount of electrical add-ons, this is clearly a concern and the reason for the dual batteries. Yes, one battery will work. Until the batteries age and it doesn't. Then everyone will blame the Jeep and not their electrical mods. (Engineers do think about what people will blame)

The question is why do people say you should have the same size batteries in parallel. Size is actually irrelevant. Resting voltage is what matters. You want the batteries to have the same resting voltage or the weaker battery will weaken the stronger battery until they are balanced, then it's a non-issue. The most likely way to have two batteries with the same resting voltage is for them to be the same size, same manufacturer, same age, same use. But it's not the only way.

That's the reason, it has nothing to do with battery size itself as power draw will balance between the two. It also goes to show that the worst possible thing you can do for battery longevity is mixing a new Main with old Aux or vice versa. They will have drastically different resting voltages regardless of their size or manufacturer.

I do have to say that the @Genesis Offroad Aux battery relocation kit that replaces both Main and Aux with two Group 25 batteries is a great option. Different size batteries is only a small problem but it is still a problem. While Aux doesn't NEED to be Group 25, it is better if it's the same size & manufacturer as the Main. It will also straighten out a lot of people's thinking if they can see Main & Aux side by side instead of Aux being a hidden mystery.
I hear what you are saying about resting voltage really being the issue here and optimization occurring when each battery's metric of this measurement most closely aligns with the other battery's measurement of resting voltage--not that relative or even identical battery size is itself the goal, but that more to point using battery size (and maybe some other tricks like swapping every now and then which battery is the main and which is the ESS one) we hope to close the gap between relative resting voltage differences. Restated, battery size (even more so than identical size) is a means to a loftier goal: minimizing resting voltage differentials.

This is why, to try to get to or approximate this state of nirvana where resting voltages are similar, I thought a larger Aux battery, even larger perhaps than the main battery, might actually be better, because as much as accessories powered during an ESS event may not draw that much current as you say, I was counterbalancing this fact with the idea that the ESS battery isn't getting simultaneously charged by the alternator during such events, while--barring engine cranks, (which in fairness are big power draw events) the main battery is getting recharged at all other times it is simultaneously taxed by appliances.

A larger ESS battery might lose voltage slower to the point where the average duration and current draw ESS event brings that battery's voltage down less, so that when the batteries are paired up at ESS conclusion, this differential is minimized.

Perhaps, more than a larger ESS battery, identically sized ones that switch off being main and aux battery might allow similar ware and tear over time so as to minimize this resting voltage differential.
 

jaymz

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I replaced both main and aux batteries mid 2021 and have been trouble free until about two months ago. I noticed I hadn't been shutting off the ESS, but the jeep wasn't shutting off either. Quick scroll through the info screen shows "start/stop not ready, battery charging". Much to my surprise - no dash warning lights of any sort, alternator is charging and no starting issues. I keep waiting for it to leave me stranded, but so far, so good. Maybe one of these days I'll look into what's going on.
 

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Reinen

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I replaced both main and aux batteries mid 2021 and have been trouble free until about two months ago. I noticed I hadn't been shutting off the ESS, but the jeep wasn't shutting off either. Quick scroll through the info screen shows "start/stop not ready, battery charging". Much to my surprise - no dash warning lights of any sort, alternator is charging and no starting issues. I keep waiting for it to leave me stranded, but so far, so good. Maybe one of these days I'll look into what's going on.
From the point ESS stopped engaging you have about 2-3 months before something critical fails. So you may want to make one of those days within that timeframe.
 

Reinen

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I hear what you are saying about resting voltage really being the issue here and optimization occurring when each battery's metric of this measurement most closely aligns with the other battery's measurement of resting voltage--not that relative or even identical battery size is itself the goal, but that more to point using battery size (and maybe some other tricks like swapping every now and then which battery is the main and which is the ESS one) we hope to close the gap between relative resting voltage differences. Restated, battery size (even more so than identical size) is a means to a loftier goal: minimizing resting voltage differentials.

This is why, to try to get to or approximate this state of nirvana where resting voltages are similar, I thought a larger Aux battery, even larger perhaps than the main battery, might actually be better, because as much as accessories powered during an ESS event may not draw that much current as you say, I was counterbalancing this fact with the idea that the ESS battery isn't getting simultaneously charged by the alternator during such events, while--barring engine cranks, (which in fairness are big power draw events) the main battery is getting recharged at all other times it is simultaneously taxed by appliances.

A larger ESS battery might lose voltage slower to the point where the average duration and current draw ESS event brings that battery's voltage down less, so that when the batteries are paired up at ESS conclusion, this differential is minimized.

Perhaps, more than a larger ESS battery, identically sized ones that switch off being main and aux battery might allow similar ware and tear over time so as to minimize this resting voltage differential.
Resting voltage only makes a difference when the batteries are newly installed. The battery with the higher resting voltage will be stressed and weakened until its resting voltage is identical with the resting voltage of the lower battery. Then they will be balanced and no more damage will be done. The problem here is that the weaker battery will drag the stronger battery down to its level. But if they're both new batteries that level won't be all that far below and the problem relatively minor.

An old and new battery is a completely different story. Their resting voltages will be vastly different. End result is the new battery will live a very stressful life and will quickly become just as bad as the old battery. Then people wonder why their new battery died very young.

An Aux battery larger than the main will still have the initial resting voltage problem. Also the Main does all the heavy lifting of cranking the engine, so why have the smaller battery do that? There's really only negatives when making Aux larger than Main and no real positives.

An argument can be made for identical size batteries. Two identical size and manufacturer batteries will nearly eliminate the initial resting voltage problem. That is a definite small plus to longevity. During cold starts Main & Aux remain linked and 2 x Group 25 > 94R + AUX14. Another plus. During warm ESS starts a larger Aux will help compensate for the drain on Main once they are reconnected. However that may just result in a smidge better MPG for a bit as the smart alternator may not go full power with the help of a larger Aux. That would require some testing.

So I'm with you on 2 identical Group 25 batteries as the sweet spot, but not a larger Aux.
 

Tangokilo

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I like my ess battery just like it is totally dead. I think it's been at least a year with no problems. It renders ess invisibly totally deactivated.
 

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The intro

We can conjecture on the exact reasons for Stellantis' decision to incorporate two AGM batteries into builds of what I believe are the most common engine configurations of the JL. I've often theorized that the dual battery design protects the main battery, to bare the bulk of the cranking power after an ESS event, and that such designs might be more critical in vehicles like the Wrangler, historically subjected to larger numbers of owner modifications, particularly with electrical current drawing appliances: from stereo systems, to lights, to winches, to off roading/camping gear etc. that drain a battery during an ESS event, not subject to replenishment from an alternator that is as motionless itself as the engine it depends on, during such ESS events.

I recently read here that the dual battery decision was fueled, of all things, by problems in testing with the entertainment system's need for more stable voltage during ESS events.

And sure, the Bronco runs ESS with one battery as does "your father's Oldsmobile," but at least for the latter, aftermarket appliances are often limited to "smart phone charge cords:" not very demanding of electrical power.

And yes Stellantis could have designed a better ESS system (or maybe pushed their entertainment system subcontractor for better product) but we would have had to pay for that. Their goal, as I see it ,was to pass an EPA test, meet CAFE standards and not get hit with whopping penalties that we'd have to share with them in purchase cost.

People who like ESS can probably fit in a phone booth. Its gas savings likely wouldn't justify the out of pocket (if not environmental as well) cost of a better design that people don't want. In fact there appear to be two camps: those who tolerate ESS and those who really hate it. And even though ESS systems do in bulk save fuel, net net, are all the used up battery components that aren't recycled and buried in land fills not merely staving off CO2 output for ground contamination, not to mention the green footprint to manufacture those batteries in the first place? Are we not simply putting off one green problem (ground contamination) to address perhaps or more pressing one (too much CO2 in the atmosphere)?

And all this comes from a green centric forum member.

The question

With all this said, many of us agree that the ESS battery is too small, and that a better design, given that the batteries are connected in parallel, might involve identically sized batteries as Shane's done so well at @Genesis Offroad, even if those equally sized batteries aren't as big as the two sizes offered for main batteries from Stellantis in their dual AGM battery JL offerings. Maybe even better, allow the batteries to periodically change roles of being the main and ESS battery, which doesn't seem like a difficult or expensive design that a bistable relay couldn't address.

But maybe the ESS battery should have actually--and maybe this is purely academic--been bigger than the main battery.

Jeep Wrangler JL The ESS battery should have been bigger, much bigger? 1710956898283-ah


We tend to need lead acid batteries (of which AGM batteries are a variant, known for their faster ability to charge and discharge like ESS events need, over mere sealed lead acid batteries) unless you can limit your travels to warmer non-freezing climates suitable for LiFEPO4 battery offerings. And AGMs tend to last longer (in time/charge cycles, if not in total lifetime amps drawn) when their depth of discharge (DOD) is minimized.

So we have this tiny battery being pushed to even further DODs than the main battery, delivering power at some times that it isn't simultaneously being replenished by an alternator (ESS events) crapping out and taking the main battery with it. Meanwhile, barring the cranking process, our larger main battery enjoys delivering power under an environment that finds a smart alternator replenishing it (and yes the ESS battery too, which also supplies power in non ESS events) real time.

Maybe, even if not cost effective, an ESS battery larger than a main would find both lasting longer. Maybe not.

Flame away!

(@THAW I hope you will add your thoughts here despite our past differences, as my issue has not been with your otherwise strong battery acumen, but more my understanding you.)
Agreed on the ESS battery ?
However, location of the AUX Battery should have been more thoroughly investigated
For most of you...ugh
I'm lucky, I have the Eco-Diesel, I don't need to remove a fender to access. Still a pain, but luckily under main battery
Lastly, Voltage information included into the dash, should have had a 2nd sensor for the AUX battery added
That's my 2 cents
 

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We were taught in class that the reason for the two battery system is voltage stabilization during the stop/start event. In our vehicles modules would randomly reset themselves due to the voltage spike from cranking after sitting at a stop light. Specifically the radio would hard restart, which obviously is a quality control problem.

They solved this by isolating the battery responsible for cranking the engine from the battery responsible for powering the interior.

What they failed to realize was the tendency for AGM batteries to fail after repeated draining. They like sitting at 90%+ SoC, so constantly dropping them to 50% just makes them die an early death. The 200CCA battery does not last long when subjected to repeated and extensive stop start events. The vehicle also is unable to monitor the effective state of charge for the aux battery outside of the first crank.

As a result we have this tiny battery that really can't power things very long, with the vehicle unable to acknowledge and charge that single battery in isolation. The battery SOC that the PCM uses to calculate battery health is both of them combined. The only time the PCM checks the aux battery directly is during the first start of the vehicle. If you've ever had a weak aux battery you'd see that the interior will flicker on the first crank attempt, but will allow cranking on the second button push. This is the PCM momentarily isolating the aux battery to determine state of health. If the aux battery is completely dead then the vehicle won't even start on the second crank, as when the interior is handed over to the aux the process just stops due to the interior having zero volts. This is why you need to put the jumper on the PDC stud to jump start the vehicle if your aux is completely dead. The aux needs to have enough voltage to at least keep the BCM/ignition switch powered up to allow that switch over to the primary battery to happen.

Anyway, using a normal sizes aux battery would go a long way to retaining proper stop/start functionality with better battery longevity. I suspect the cost of this is the primary reason it wasn't implemented. You're talking $100+ onto every build cost here, and the guys at corporate will balk at a 50 cent increase.

In reality stop start is just complete dogshit and should've never been implemented in the first place, but that ship sailed long ago. I have no damn clue why the EcoDiesels aux battery location wasn't used on the other engines. Remove the primary battery and boom there it is. The fact they didn't bother fixing it with the 2024 refresh is also mind boggling. I guess they'd have to make the wiring harnessing going to the PDC longer and that's too much $. I suspect the EcoDiesel development team had a larger budget to make it work.

I like my ess battery just like it is totally dead. I think it's been at least a year with no problems. It renders ess invisibly totally deactivated.
I assume you mean you have a "Stop start unavailable, battery charging message" in your EVIC. It isn't totally dead or your vehicle wouldn't start. It has enough voltage to keep powering the interior, but it's combined voltage with your primary is simply too low to allow stop start functionality. I also assume it isn't dead enough to through the auto s/s warning light with a battery 'b' performance code, as you said it's "invisible". You will go out one morning and your Jeep will not start, or you will blow your z-case fuse randomly. I suggest you fix the problem sooner rather than later. There are plenty of topics on this forum on how to delete the aux battery entirely. Highly recommended.
 

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eTorque engine option is a mild hybrid system that replaces the traditional alternator with a 48-volt battery-power, belt-drive motor generator. This increases performance, efficiency, payload, and towing capabilities.
 

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From the point ESS stopped engaging you have about 2-3 months before something critical fails. So you may want to make one of those days within that timeframe.
Maybe. But that wasn’t the case with the original batteries. Bought the Jeep used and the ESS never worked. Long boring story short, I changed the batteries about a year later and only realized there was two when I went looking for replacements.
 

alphawolff

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eTorque engine option is a mild hybrid system that replaces the traditional alternator with a 48-volt battery-power, belt-drive motor generator. This increases performance, efficiency, payload, and towing capabilities.
The eTorque system was actually designed purely to solve the stop/start issue, which is does fantastically well. The eTorque is pretty damn sweet overall.
 

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Hate to mess up the train of thought here but…..

Like many others, I DELETED my auxiliary battery after being stranded several times in the first year with my brand new Jeep.

We’re heading on at least two years without an auxiliary battery and hundreds of cranks so that kinda disproves “clean voltage” being a reason for the auxiliary battery.

It also shows relocation and/or resizing isn’t of much value.

Dual batteries are good for increasing CCA capacity or maybe powering dozens of light bars with the engine off but seriously - If a Jeep needs dual batteries just to power the vehicle’s FOB detector and keep the channels programmed in “some” Jeeps, there’s something wrong.

If it were battery size/mismatch, ALL Jeeps would be affected.

If it’s a design discrepancy, it would affect ALL of the same design, not just a few which is why I am certain several of us have a failed “something”.

Theres a parasitic draw in all Jeeps to power keyless entry, radio programming and the sentry but I think that draw is more pronounced in some Jeeps than others.

Like everyone else, mine still has the draw, it just has ESS disabled, the auxiliary battery gone and Fuse 42 pulled to reduce the dreaded “click click click” and Christmas tree lit dash.

Maybe it’s intermittent diode bleed in the alternator that only affects Jeeps have crossed a creek or flexed more than curb height, I dunno.

That said, I think removing, resizing, relocating or constantly replacing the batteries is akin to pulling the bulb from a warning light in the dash. It doesn’t fix the root cause, it just removes the glare of annoyance.
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