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Do I "need" the auxiliary battery

rickinAZ

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With my Tazer defeating the ESS, can I happily run with a bad/dead auxiliary battery or do I need to replace it for some other reason? I ask, because I appear to have a battery issue (has needed jump starting a few times lately) and I want to make sure that, if it is a battery problem, I can isolate it to the main battery. I plan to have it tested at Autozone today but I'm not sure if their diagnostic device will detect auxiliary vs main battery issues.
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With my Tazer defeating the ESS, can I happily run with a bad/dead auxiliary battery or do I need to replace it for some other reason? I ask, because I appear to have a battery issue (has needed jump starting a few times lately) and I want to make sure that, if it is a battery problem, I can isolate it to the main battery. I plan to have it tested at Autozone today but I'm not sure if their diagnostic device will detect auxiliary vs main battery issues.
@rickinAZ

I encourage you not to go to Autozone as they will not separate the batteries out. Will be a waste of your time.

You have a warranty on your 2021 so go the dealer. Speak to the Service Manager (not the Service Writer) and politely ask that they "load test" each battery, show you each print out.... each print out in regard to the 2 batteries. Without seeing the 2 print outs you will not be sure if they actually took the time to do the tests at all or on both. Do know that they will have your JL for hours as it takes time to separate out, charge and load test both.

NO, you do not want to run with a depleted/iffy Aux battery.

You did not defeat ESS ... you just have an electronic device doing your simple button pushes for you.
 

calemasters

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You do need both a good main battery and a good auxiliary battery.

I was getting warning emails from Jeep about low system voltage. So every morning, after my Jeep set overnight, I was measuring battery voltage with my Fluke 87, with both engine and ignition off. This was with both batteries connected. I was getting readings of ~ 11.2 volts. I don't like going to the dealer, plus I wanted to install one of the best automotive batteries I could find. So I installed the Odyssey Performance 94R-850 main battery as well as a new auxiliary AGM size 12 battery (since the aux battery has received so much bad press here on the forum). I don't know which battery was causing the low voltage issue, but I didn't care since I was on a mission to replace both. The fully charged, resting & disconnected Odyssey voltage is 12.8 volts. Yeah for virgin lead! With both batteries installed, I have been checking the battery voltage each morning since I want to make sure there are no unexpected parasitic current draws.

I have continued to check battery voltage, over a 1 month period, and now the resting, connected battery voltage is at 12.74 volts (after a 48 hour sitting period) whereas before it was 11.2 volts. So I think I fixed my low voltage problem. Hopefully, no more warning emails from Uconnect / Jeep. :)
 
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rickinAZ

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You do need both a good main battery and a good auxiliary battery.

I was getting warning emails from Jeep about low system voltage. So every morning, after my Jeep set overnight, I was measuring battery voltage with my Fluke 87, with both engine and ignition off. This was with both batteries connected. I was getting readings of ~ 11.2 volts. I don't like going to the dealer, plus I wanted to install one of the best automotive batteries I could find. So I installed the Odyssey Performance 94R-850 main battery as well as a new auxiliary AGM size 12 battery (since the aux battery has received so much bad press here on the forum). I don't know which battery was causing the low voltage issue, but I didn't care since I was on a mission to replace both. The fully charged, resting & disconnected Odyssey voltage is 12.8 volts. Yeah for virgin lead! With both batteries installed, I have been checking the battery voltage each morning since I want to make sure there are no unexpected parasitic current draws.

I have continued to check battery voltage, over a 1 month period, and now the resting, connected battery voltage is at 12.74 volts (after a 48 hour sitting period) whereas before it was 11.2 volts. So I think I fixed my low voltage problem. Hopefully, no more warning emails from Uconnect / Jeep. :)
Thanks for the informative/complete answer. How challenging is the aux replacement for a ham-fisted DIYer? Any tips?
 

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Thanks for the informative/complete answer. How challenging is the aux replacement for a ham-fisted DIYer? Any tips?
Rick, since you have a diesel it is easy to access the auxiliary battery after removing the main battery. Pull the main battery and there is an access panel beneath it with a couple of screws. Remove this and you will have easy access to the aux battery. You don't need to pull anything from the fender liner.
 
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rickinAZ

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Rick, since you have a diesel it is easy to access the auxiliary battery after removing the main battery. Pull the main battery and there is an access panel beneath it with a couple of screws. Remove this and you will have easy access to the aux battery. You don't need to pull anything from the fender liner.
I like your response. Everything else that I've read makes replacing the auxiliary battery sound difficult. Is it really that simple on a diesel?

EDIT: I found this video (https://www.jlwranglerforums.com/fo...ent-than-gasoline-engines.87942/#post-1869894)

Troy and Allen, you've made my day!
 
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morlan52

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I like your response. Everything else that I've read makes replacing the auxiliary battery sound difficult. Is it really that simple on a diesel?

EDIT: I found this video (https://www.jlwranglerforums.com/fo...ent-than-gasoline-engines.87942/#post-1869894)

Troy and Allen, you've made my day!
Yup it is that easy - we are lucky as diesel owners 😁 Jeep did not have the right mindset when they designed the fuse distribution to be located over that battery in the other engines. They certainly weren't thinking about "ease of maintenance".

I was having some battery issues a few months ago and was able to quickly pull both batteries in the parking lot of Autozone and have them individually load-tested.
 

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Go through the fender well. You can easily remove the fender liner and access the aux battery that way.
No. It's a diesel. It's under the main battery.
 

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Strangely my JL doesn't shut off ( ESS ) anymore when stopping. I used to keep pressing the ESS off button when I first got it, but eventually it just stopped shutting the engine off at every stop sign...

It's been like this for over a year... When I check the ESS Screen it says it's not fully charged so ESS would not enable. I've driven back and forth to Florida and it still say's charging - not ready yet.
 

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Strangely my JL doesn't shut off ( ESS ) anymore when stopping. I used to keep pressing the ESS off button when I first got it, but eventually it just stopped shutting the engine off at every stop sign...

It's been like this for over a year... When I check the ESS Screen it says it's not fully charged so ESS would not enable. I've driven back and forth to Florida and it still say's charging - not ready yet.
Replace both batteries.
 

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@rickinAZ

I encourage you not to go to Autozone as they will not separate the batteries out. Will be a waste of your time.

You have a warranty on your 2021 so go the dealer. Speak to the Service Manager (not the Service Writer) and politely ask that they "load test" each battery, show you each print out.... each print out in regard to the 2 batteries. Without seeing the 2 print outs you will not be sure if they actually took the time to do the tests at all or on both. Do know that they will have your JL for hours as it takes time to separate out, charge and load test both.

NO, you do not want to run with a depleted/iffy Aux battery.

You did not defeat ESS ... you just have an electronic device doing your simple button pushes for you.
If I'm using the jumper N1 to N2 and the aux takes a dump... Does it matter?
 

loracekim

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You do need both a good main battery and a good auxiliary battery.

I was getting warning emails from Jeep about low system voltage. So every morning, after my Jeep set overnight, I was measuring battery voltage with my Fluke 87, with both engine and ignition off. This was with both batteries connected. I was getting readings of ~ 11.2 volts. I don't like going to the dealer, plus I wanted to install one of the best automotive batteries I could find. So I installed the Odyssey Performance 94R-850 main battery as well as a new auxiliary AGM size 12 battery (since the aux battery has received so much bad press here on the forum). I don't know which battery was causing the low voltage issue, but I didn't care since I was on a mission to replace both. The fully charged, resting & disconnected Odyssey voltage is 12.8 volts. Yeah for virgin lead! With both batteries installed, I have been checking the battery voltage each morning since I want to make sure there are no unexpected parasitic current draws.

I have continued to check battery voltage, over a 1 month period, and now the resting, connected battery voltage is at 12.74 volts (after a 48 hour sitting period) whereas before it was 11.2 volts. So I think I fixed my low voltage problem. Hopefully, no more warning emails from Uconnect / Jeep. :)
From my experience and several others you do NOT need the auxillary battery.
It's a pain to deal with, makes jump starting difficult, makes battery replacement more costly almost always kills the main battery when it dies and is only really needed in my opinion if you use ESS.
What I and other have done is remove it and reroute the positive up and connect to the main battery positive terminal. I left the ground from the aux battery un connected. But with extension added u could connect that to the main ground terminal also.
Works great no warnings and now it acts like a old fashion battery for jump starting, drip charger etc.
I did upgrade to a AGM 850 CCA but work with factory battery fine.
Do NOT use ESS since at a long stop it may drain your main battery to low to start again. I use a taser programmer to shut it off.
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