My thoughts on the auxiliary battery

[Lost1wing]

Crap, I can't even get away from her name or images or some crap about her on a Jeep forum! Good grief, sex/sultry sells. Ugh, can't stand her. It's hard to even pull up a browser page with current news without her showing up. Enough already!

That was definitely a joke! I'm not a fan. Sorry for mentioning the name.

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[yoda13]

Interesting. Mine activated a couple of times and I got in the habit of pushing the button at startup.
Keep in mind that it's fairly finicky about meeting certain criteria to be able to activate.
Warmed engine, not too cold or hot outside, firm braking to a stop.

My ESS still activates, even with the Aux battery disconnected.

 

[Rob_R]

The batteries aren't remaining at that voltage - the truck is replacing what was taken out during the startup sequence - via starter and electronics and so on. It also uses battery temperature and historical data sent to the BCM from the IBS via the Lin to determine how to set voltage.
It will always make up for what you take out during the startup sequence of events, but once that's done, if it's satisfied based on the data, current voltage and other factors, it will lighten the load on the engine accordingly. It's in maintenance mode at that point.

Thanks for the explanation and correction, Bill. I will continue monitoring the alternator activity. I did find it odd that the alternator did not behave the same after a few days of around town driving without being plugged into the charger/maintainer. If I am not going to drive the JT for a day or two, I usually plug in the charger/maintainer.

What I mean by this when the charger/maintainer is first removed from the truck, the alternator voltage would remain constant (13.7- 13.8V), no matter what the throttle or brake position is. Over the course of approximately 2 days, the alternator voltage will slowly drop to 12.7-12.8V without any smart alternator activity.

On the second or third day of driving and the truck not being plugged in to the charger/maintainer, the alternator starts reacting to throttle and brake position. The alternator would settle in at around 12.7-12.8V while on-throttle. While during off-throttle and braking, the alternator would do it's smart battery thing and the voltage would jump up to 14.X.

I could guess at what is happening in the above observations but that may expose my lack of knowledge in this area.

 

[Andy29847]

Amazing. That's sure different than my experiences and that of those I've talked to.
Referring back to while I was in a NAPA store a few months back - getting a battery replaced (one that lasted almost 4 years! Amazing! - but for a 1982 car) guys were in there complaining that they were having trouble getting a battery to last even 4 years. They were not Jeep people.
My son had a problem with his Fusion after about 3 years - battery failure.
4xe owners complain of battery issues - no, not the HV battery, but the 12 volt battery.
And the kicker is - there is no ESS and no aux battery! The 12 volt battery, exactly like the main battery in our JTs, doesn't last. In some cases, they don't make it a year, others are saying that after 2 or 3 years the 12 volt battery craps out.
So we can't blame ESS or the aux battery or whatever.
It's a combination of things, a stack-up of issues.
Guys with ordinary cars and trucks complaining about battery life.
My son's Fusion - battery died pretty quickly.
4xe owners having batteries fail after anywhere from 2 months to 2 or 3 years.
And yet the batteries in my son's Compass weren't problematic. The batteries in my wife's WK2 went 3 years and crapped out. Battery in my SX4 - almost 4 years and crapped out.

You cut short my comment. I wrote: "The quality of the Mopar batteries and the design of the battery systems in our Jeeps are called in to doubt by the number of questions and complaints from Jeep owners. I've never had another vehicle where batteries were an issue. "

Instead of just writing "batteries were an issue (though ultimately that is the problem), " I should have added in something about the multiple batteries and the system design. I'll do better.

 

[chorky]

The parasitic draw isn't really a flawed electrical design. It is the next generation owners and or designers coming up with more demands on the electrical systems.

In 1966 and you turned the key off the car was dead with the exception of the dome light. It went off when the doors closed. Well, it had an analog clock.

Later years added alarms. Then lights remain on then the body modules remained on for a period. More wireless gadgets were added. Now, computers in some just stay on. The demand for power is outrageous all to make you feel good. It all comes with a price and that is battery life.

I just replaced an original battery in a 2005 tractor. That battery has one function and that is to start the tractor. It may be a different battery than that of a car battery but 18 years is pretty good.

I wonder how long until Jeep and other manufacturers trying to cater to the 'overland' crowd will redesign their ESS system so it runs off of a battery bank that is totally separated from the main vehicle electrical system. Sorta like a 'house' battery we use now. Think about it. There are plenty of things that occur in a ESS event that really dont need to be tied to the main battery at all. Especially if there is a quality DC/DC charger incorporated into the vehicle already - like what they do for the 110v plugs. I think if Jeep was smart they would look into something like this. Run the aux switches off of a 'house' battery, even the radio with an eternal mounted waterproof speaker on the tailgate or something. I bet people would go wild over it if it was robust enough, was expandable, and wasn't in some crazy stupid location. There are endless opportunities for something like this. Then the main vehicle systems wouldn't ever have to be touched, releasing some liability aspects. Grated they probably wouldn't make a great system right off the bat - similar to how the 110v plugs are inadequate for most practical uses. But it does surprise me that nobody has hinted at looking into this for future vehicle's.

 

[ShadowsPapa]

I wonder how long until Jeep and other manufacturers trying to cater to the 'overland' crowd will redesign their ESS system so it runs off of a battery bank that is totally separated from the main vehicle electrical system. Sorta like a 'house' battery we use now. Think about it. There are plenty of things that occur in a ESS event that really dont need to be tied to the main battery at all. Especially if there is a quality DC/DC charger incorporated into the vehicle already - like what they do for the 110v plugs. I think if Jeep was smart they would look into something like this. Run the aux switches off of a 'house' battery, even the radio with an eternal mounted waterproof speaker on the tailgate or something. I bet people would go wild over it if it was robust enough, was expandable, and wasn't in some crazy stupid location. There are endless opportunities for something like this. Then the main vehicle systems wouldn't ever have to be touched, releasing some liability aspects. Grated they probably wouldn't make a great system right off the bat - similar to how the 110v plugs are inadequate for most practical uses. But it does surprise me that nobody has hinted at looking into this for future vehicle's.

Talk about adding weight and complexity.........
A battery pack? More weight, a lot more money.
And to tie it all together, a lot more complexity. Heck, people don't even "get" the simple system that exists now - adding anything else and you'll lose even more to the "I don't get it" crowd.
What do you have tied to the aux switches that needs to be powered up during an ESS event?
Why are the aux switches part of the discussion?
What is there that doesn't need to be tied to the main battery?
You realize that they have already split things apart - and thus the aux battery.
So are you suggesting that instead of the aux battery, they use a battery pack somewhere else, make it larger, and use a DC/DC charger to maintain it?
Where would you put it? (keeping in mind the cabling needed to tie it all together)

Naw, leave that conglomeration and complexity and weight to the people who WANT it, don't make the thing more complex and expensive than it is. First time out with something like that and you'd have a lot of "but they did it wrong" - so why? There are so very few that even use these that way. Is it worth the engineering, the EPA and CAFE things, going through more certifications - for a very few?

I say - if you want such a system - then install it. But 97+% wouldn't ever care.

 

[chorky]

Talk about adding weight and complexity.........
A battery pack? More weight, a lot more money.
And to tie it all together, a lot more complexity. Heck, people don't even "get" the simple system that exists now - adding anything else and you'll lose even more to the "I don't get it" crowd.
What do you have tied to the aux switches that needs to be powered up during an ESS event?
Why are the aux switches part of the discussion?
What is there that doesn't need to be tied to the main battery?
You realize that they have already split things apart - and thus the aux battery.
So are you suggesting that instead of the aux battery, they use a battery pack somewhere else, make it larger, and use a DC/DC charger to maintain it?
Where would you put it? (keeping in mind the cabling needed to tie it all together)

Naw, leave that conglomeration and complexity and weight to the people who WANT it, don't make the thing more complex and expensive than it is. First time out with something like that and you'd have a lot of "but they did it wrong" - so why? There are so very few that even use these that way. Is it worth the engineering, the EPA and CAFE things, going through more certifications - for a very few?

I say - if you want such a system - then install it. But 97+% wouldn't ever care.

Come on man it's Sunday what's with all the questions??????????????????????????????

What do you have tied to the aux switches that needs to be powered up during an ESS event? Me - nothing. But others might have a need
Why are the aux switches part of the discussion? - some people use the aux switches to power things like a fridge, radio, etc.
What is there that doesn't need to be tied to the main battery? well, everything not essential for a running engine doesn't need to be tied to the main battery.... And no I dont mean things like the ECU, I mean things like the blower motor fan, radio, etc. Haven't you ever run your radio at an old drive in movie before?
You realize that they have already split things apart - and thus the aux battery. yep
So are you suggesting that instead of the aux battery, they use a battery pack somewhere else, make it larger, and use a DC/DC charger to maintain it? yep. Essentially. For sure this would be more complicated in some ways. But in other ways it will make things easier to understand. Sorta how like now with the aux battery totally bypassing the IBS, and with a heck of a lot of unnecessary troubleshooting needed to identify specifically if the aux battery is bad or the main battery is bad, charging them both separate, etc.. If a DC/DC was used, primarily for the ESS systems, then it would make diagnosing easier since you wouldn't have two batteries in parallel, but only one receiving input from the IBS. It might also open the door for Jeep to expand their aux switches, and maybe throwing in a 'overland' option of half a dozen switches or so in the bed.
Where would you put it? (keeping in mind the cabling needed to tie it all together) maybe in the cab under the passenger rear seat, or possibly between the frame rails (not really a great location) - there is also a fair amount of open unused space between the outer sheet metal of the truck bed and the inner sheet metal - I'm sure there is a way to put something in there, someone here already did that actually.

 

[Lost1wing]

Then your point is pointless, just like your not a jeep engineer so why would I listen to what someone says in a thread on a forum.

In the real world, engineers rely on feedback from technicians. They do their best to design systems, but sometimes it just doesn't work out.

They get their feelings hurt when they are told their design has a flaw. You can give them the fix, but they would rather spend another $100k to fix their own problem. We found it easier and faster not to give them our recommendation, so that they feel comfortable using the easy fix.

This forum has plenty of engineer types and very intelligent individuals. This is just information for us to use and discuss, take it or leave it.

 

[Andy29847]

Then your point is pointless, just like your not a jeep engineer so why would I listen to what someone says in a thread on a forum.

If I was a churlish kind of guy, I might write that YOU’RE not an English teacher. I’m sorry for even thinking like that.

 

[Jeeperjamie]

If I was a churlish kind of guy, I might write that YOU’RE not an English teacher. I’m sorry for even thinking like that.

I'm not an English teacher so you got something right.

 

[Glad Jeeper]

Are there any other functions the aux battery is used for beside the start/stop function?

 

[Lost1wing]

No one would ever mistake me for being an English teacher, nor would I call anyone

Are there any other functions the aux battery is used for beside the start/stop function?

Correct me if I am wrong, but the Aux battery is only a piece of the puzzle. It is used to keep the electronics alive when the engine is off during a start stop event.

Disconnecting the aux negative, and pulling f42 only prevents the pcr from isolating the two batteries during the start up test. ESS is still active, using only the main battery. The only benefit of this would be if your aux battery was bad and dragging down your main. Potential problem with doing this is the computers seeing the voltage drop during a start stop event. If you select start stop to be off, (doesn't matter how you do it), you won't have that risk during a stop start event.

 

[ErylFlynn]

When my warranty is over I am likely switching to a dual battery setup from Genesis. Give me more capacity and remove the extra work to replace the little one. And with me planning to need to charge a scooter in the back the extra capacity would be useful.

 

[Andy29847]

Are there any other functions the aux battery is used for beside the start/stop function?

The aux battery is used to power some devices (primarily in the cab) whenever a stop/start event occurs. The reason for using 2 batteries is debatable. Some here say that the second battery protects the sensitive electronic equipment from a low voltage condition caused by current drain when the Jeep is cranked. The literature I have read indicates that the purpose of splitting the aux battery during a stop/start event is to shield the main battery and alternator from excessive starting loads. I think excessive starting loads is most correct. I believe that if I use a single battery that is equal to the 2 Mopar provided batteries, I can abandon the aux battery and the complications (and expense) of using a 2 battery system.

Except for a stop/start event, the 2 batteries an a JL/JT Jeep are hooked together and function as a single battery.

 

[Lost1wing]

The aux battery is used to power some devices (primarily in the cab) whenever a stop/start event occurs. The reason for using 2 batteries is debatable. Some here say that the second battery protects the sensitive electronic equipment from a low voltage condition caused by current drain when the Jeep is cranked. The literature I have read indicates that the purpose of splitting the aux battery during a stop/start event is to shield the main battery and alternator from excessive starting loads. I think excessive starting loads is most correct. I believe that if I use a single battery that is equal to the 2 Mopar provided batteries, I can abandon the aux battery and the complications (and expense) of using a 2 battery system.

Except for a stop/start event, the 2 batteries an a JL/JT Jeep are hooked together and function as a single battery.

The main battery can handle it all. The aux battery will power computers , blower fan radio until it is detected to be at a low state. Then you would get the battery charging message. Without the aux, you would have the possibility of a no start due to consuming your batteries power.

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