Jumperless Aux Battery Bypass

[andy29847]

Removed fuse and cable again and here's the results
Auto start light on still
No others on this time.
Voltage on dash reads 13.9

Put fuse/cable back and drove about an hour. Voltage at 13.4 (which I know is low)
Auto s/s light on. Don't have a meter to double check voltage. Will have a meter tomorrow to check more. Thanks again

You are reading voltage with the truck running which means you are reading charging voltage, not battery voltage.

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[andy29847]

Here is an example of voltage readings from the dash display. My Jeep is a 2020. My stop/start quit working last November. After 3 trips to the dealer, the main battery was replaced. The dealer used an Interstate battery that is 790CCA (when I replace this battery, I plan to use the Everstart H7 battery from Walmart - 850CCA). My Jeep has the aux battery disconnected.

Frist AM, ignition on run, engine off

Voltage immediately after cranking the engine.

Voltage 15 seconds after cranking the engine (charging voltage)

I was surprised how low the battery measured after sitting overnight. Of course, 12.1v is not the true voltage number. It's the voltage pulled down by the load of the Jeep's systems. I would need to disconnect the battery and measure with a meter to get the "true" rating. I was pleased that the voltage barely fell off after cranking. For me, this is the surest sign of a good battery. My charging voltage when I had both batteries connected was always 14.7v. When I disconnected the aux battery, the initial charging voltage dropped to 14.4v. If I drive for an hour, the charging voltage gradually goes down to 13.9v. I deem this normal behavior.

 

[Rhinebeck01]

Here is an example of voltage readings from the dash display. My Jeep is a 2020. My stop/start quit working last November. After 3 trips to the dealer, the main battery was replaced. The dealer used an Interstate battery that is 790CCA (when I replace this battery, I plan to use the Everstart H7 battery from Walmart - 850CCA). My Jeep has the aux battery disconnected.

Frist AM, ignition on run, engine off

Voltage immediately after cranking the engine.

Voltage 15 seconds after cranking the engine (charging voltage)

I was surprised how low the battery measured after sitting overnight. Of course, 12.1v is not the true voltage number. It's the voltage pulled down by the load of the Jeep's systems. I would need to disconnect the battery and measure with a meter to get the "true" rating. I was pleased that the voltage barely fell off after cranking. For me, this is the surest sign of a good battery. My charging voltage when I had both batteries connected was always 14.7v. When I disconnected the aux battery, the initial charging voltage dropped to 14.4v. If I drive for an hour, the charging voltage gradually goes down to 13.9v. I deem this normal behavior.

@andy29847

Unfortunately, I believe you deem wrong...

Read over you post.... Your Main battery, based on what you posted is not in terrific condition..
(Or you drive very little and the alternator is not being given enough time to maintain the 12v)

12.1 is not typical in the am for a healthy Main that has sat all night. (12.6, 12.7 is typical)

11.7 after start..... not typical..

When driving you should see, gradual dips to say 13.2, 13.4 or a bit lower... then goes up and down... (up to say 14.1 or so.)

You might want to move to that H7, sooner rather then later.

https://www.jlwranglerforums.com/forum/threads/??-main-battery-replacement-talk-jl-jt-?.100534/

 

[mdkautzman]

My 2020 JT aux cable was on the left side looking from the front in. My 2021 JL it's the right cable with the larger tab. They are not consistent from year to year or model from what I've seen. Just make sure your disconnecting the smaller diameter of the two.

 

[Rhinebeck01]

My 2020 JT aux cable was on the left side looking from the front in. My 2021 JL it's the right cable with the larger tab. They are not consistent from year to year or model from what I've seen. Just make sure your disconnecting the smaller diameter of the two.

Aux negative cable on the Main's negative side, is always the smaller diameter cable of the two found there.

Read here:
https://www.jlwranglerforums.com/forum/threads/ess-battery-cable-change.86624/

 

[andy29847]

@andy29847

Unfortunately, I believe you deem wrong...

Read over you post.... Your Main battery, based on what you posted is not in terrific condition..
(Or you drive very little and the alternator is not being given enough time to maintain the 12v)

12.1 is not typical in the am for a healthy Main that has sat all night. (12.6, 12.7 is typical)

11.7 after start..... not typical..

When driving you should see, gradual dips to say 13.2, 13.4 or a bit lower... then goes up and down... (up to say 14.1 or so.)

You might want to move to that H7, sooner rather then later.

https://www.jlwranglerforums.com/forum/threads/??-main-battery-replacement-talk-jl-jt-?.100534/

Thanks for the feedback. The JLU is not a daily driver and most of the trips are short. I "deemed" it OK because the battery is near new (optimistic - I know), the Jeep cranks like expected, and the stop/start goes active as soon as the temps reach an acceptable level. Still, I was surprised how low the battery reading was, even with the load of the Jeep's systems. I just went outside, isolated the battery, and checked it with my voltmeter. This reading was 12.48v. This is still lower than I expected, and probably reflects the way I use the Jeep. BTW, the battery is already an H7.

One of the benefits of deleting the aux battery is that the performance of the battery/starting system is nearly the same as all the cars I have had for 50 years. I almost think I understand it.

 

[Rhinebeck01]

Thanks for the feedback. The JLU is not a daily driver and most of the trips are short. I "deemed" it OK because the battery is near new (optimistic - I know), the Jeep cranks like expected, and the stop/start goes active as soon as the temps reach an acceptable level. Still, I was surprised how low the battery reading was, even with the load of the Jeep's systems. I just went outside, isolated the battery, and checked it with my voltmeter. This reading was 12.48v. This is still lower than I expected, and probably reflects the way I use the Jeep. BTW, the battery is already an H7.

One of the benefits of deleting the aux battery is that the performance of the battery/starting system is nearly the same as all the cars I have had for 50 years. I almost think I understand it.

Your JL would benefit by having a battery tender/maintainer hooked up to it while it sits there unused..... or at least hook one up for a few hours til tender says aok, every 5 days or so.

Your Main is going to deplete further and further if you don't drive it lots or use a a battery tender/maintainer on it. You don't want to delete so much that you chance a no start scenario.

What H7 is installed... You mentioned an Interstate.. Is it an Interstate MTX-94R/H7 80 Ah AGM 850 CCA ?

 

[andy29847]

What H7 is installed... You mentioned an Interstate.. Is it an Interstate MTX-94R/H7 80 Ah AGM 850 CCA ?

Dealer installed replacement - MTP-94R/H7 790 CCA

 

[andy29847]

Your JL would benefit by having a battery tender/maintainer hooked up to it while it sits there unused..... or at least hook one up for a few hours til tender says aok, every 5 days or so.

Your Main is going to deplete further and further if you don't drive it lots or use a a battery tender/maintainer on it. You don't want to delete so much that you chance a no start scenario.

The dealer installed my new main battery when my mileage was ~35,500. I wasn't happy that they didn't replace both batteries, which was a driving force behind my considering deleting the aux battery. I drove the vehicle for a couple of month with the old aux battery and new main battery connected in parallel as per the factory. I wonder if this could be the cause of the lower than expected voltage readings I have now? I'll charge the battery and check it again.

 

[Rhinebeck01]

The dealer installed my new main battery when my mileage was ~35,500. I wasn't happy that they didn't replace both batteries, which was a driving force behind my considering deleting the aux battery. I drove the vehicle for a couple of month with the old aux battery and new main battery connected in parallel as per the factory. I wonder if this could be the cause of the lower than expected voltage readings I have now? I'll charge the battery and check it again.

You said "Dealer installed replacement - MTP-94R/H7 AGM 790 CCA"

That Interstate MTP-94R/H7 battery your dealer installed is not , again not..... an AGM battery. It is a flooded battery. Dealer cheaped out...
https://www.interstatebatteries.com/products/mtp-94r/h7-1

Next time get an AGM H7.

Anyway ...Ideal would have been to bypass the Aux battery the same day the dealer threw in the new Main battery

Iffy, Aux battery hooked up in parallel with the new Main like it was, had a negative impact on the new Main.

 

[andy29847]

You said "Dealer installed replacement - MTP-94R/H7 AGM 790 CCA"

That Interstate MTP-94R/H7 battery your dealer installed is not , again not..... an AGM battery. It is a flooded battery. Dealer cheaped out...
https://www.interstatebatteries.com/products/mtp-94r/h7-1

Next time get an AGM H7.

Anyway ...Ideal would have been to bypass the Aux battery the same day the dealer threw in the new Main battery

Iffy, Aux battery hooked up in parallel with the new Main like it was, had a negative impact on the new Main.

I looked it up on an auto parts site before I posted and they said AGM. I checked on the Interstate site (which mush have been what you did) and they say it is not. Of course, my dealer should not have mixed the 2 types of batteries. That may be why my charging voltage always showed 14.7 when I was using both batteries. I think I'll throw a fit at the dealer.

 

[CarbonSteel]

Calling @Rhinebeck01:

So the @! (service ESS) light came on again today and (for my JLUR) I have the added bonus of the check engine light coming on and the engine running rough as crap. Codes thrown are service ESS and left engine bank running lean.

I disconnected the Auxiliary negative, pulled F42, and cleared the codes. All back to normal. I have two questions:

1. I find it hard to believe that I have another failed auxiliary battery in such a short time frame, but everything checked out--F42 was good and N3 is good as well. What else could this be--do I REALLY have another bad auxiliary?

2. I am seeing voltage in the 13.0 to 13.3 range and I am assuming that I am seeing the voltage of the main battery now that the aux is separated. Is that correct and is that voltage what I should be seeing?

As always thanks in advance for your help!

 

[Rhinebeck01]

Calling @Rhinebeck01:

So the @! (service ESS) light came on again today and (for my JLUR) I have the added bonus of the check engine light coming on and the engine running rough as crap. Codes thrown are service ESS and left engine bank running lean.

I disconnected the Auxiliary negative, pulled F42, and cleared the codes. All back to normal. I have two questions:

1. I find it hard to believe that I have another failed auxiliary battery in such a short time frame, but everything checked out--F42 was good and N3 is good as well. What else could this be--do I REALLY have another bad auxiliary?

2. I am seeing voltage in the 13.0 to 13.3 range and I am assuming that I am seeing the voltage of the main battery now that the aux is separated. Is that correct and is that voltage what I should be seeing?

As always thanks in advance for your help!

With the Aux disconnected, the voltage you see displayed when vehicle is not running is in regard to the Main. When vehicle is running that voltage displaying is alternator.

Give it a few days and see if you have another event..

 

[Sturtzy]

Battery tested good can be a trap. Our Jeeps seem to go funky when the battery gets around 12.4v. 12.4 is a good test for most batteries (50-70% life). With the aux negative unhooked, and after the Jeep has been sitting for a couple of hours, set it to run without starting it (on my Jeep, with the proximity key, I press the start button without putting my foot on the brake. The first press should go to aux, the second should go to run). Check the voltage display on your dash voltmeter. Answer back with your findings.

So here's what I did this morning 6:55am.
Ignition in aux
dash voltage reads 12.4 v (which is low in my opinion)
Removed F42 fuse and disconnected aux. bat neg wire.
battery voltage reads 12.2 at 5:54 pm in aux mode.
Started and Auto s/s light comes on.
replaced fuse and hooked up battery cable.
Started and while at idle battery (charge)voltage is 14.1
Thanks

 

[andy29847]

Calling @Rhinebeck01:

So the @! (service ESS) light came on again today and (for my JLUR) I have the added bonus of the check engine light coming on and the engine running rough as crap. Codes thrown are service ESS and left engine bank running lean.

I disconnected the Auxiliary negative, pulled F42, and cleared the codes. All back to normal. I have two questions:

1. I find it hard to believe that I have another failed auxiliary battery in such a short time frame, but everything checked out--F42 was good and N3 is good as well. What else could this be--do I REALLY have another bad auxiliary?

2. I am seeing voltage in the 13.0 to 13.3 range and I am assuming that I am seeing the voltage of the main battery now that the aux is separated. Is that correct and is that voltage what I should be seeing?

As always thanks in advance for your help!

Voltages in the 13-14 range are measurements of charging voltage.

let you Jeep sit overnight. In the morning, press the start button twice without putting your foot on the brake to put you ignition in the run condition with the engine off. Scroll through your dash gauges to you voltmeter and the voltage you see is the main (aux still disconnected) minus the system load (.3-.4 tenths on my Jeep). Leave the voltmeter up and crank your Jeep. Note the voltage as it cranks. Mine goes to 11.7 which is OK but maybe not good. Leave the engine running and watch the voltmeter. You should reach charging voltage in 15 seconds or so. My Jeep charges in the 13.9 - 14.4 range using just the main battery. I’ve been working on my Jeep the past 24 hours and made these test and discussed them here on pages 27 and 28. I started out think all was well but with the help of Rhinebeck, I know that my dealer installed a flooded lead acid battery last JAN instead of the required AGM battery (2 batteries connected together need to be the same type). If it is easy, tell us which batteries you have.

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