Auxilary Battery Died then Main Battery Died - Important Info

[ShadowsPapa]

Both of your meters are measure the combined voltage of the 2 batterries connected in parallel, just at different points in the circuit. You will have to seperate the batteries to get the individual battery voltage readings.

^^^
What Jerry said - however I find the differences shown in that pic interesting. I have always wanted to measure the VOLTAGE DROP across the wiring between the two batteries and through the PCR - and if you have two very accurate meters (which I suspect these are not necessarily) it would be only a 0.1 volt drop with no load.

I use the NOCO genius 5 with the quick connect eyelet pigtail (replacing the alligator clamps), permanently attached to the positive post and the ground bolt on the passenger fender.
I also added SAE pigtails to attach Battery Tender volt meters so I can monitor SOC on the Aux and Crank batteries.

I still think it's worth what you have done with those meters. What I'd do if it was mine since you are showing a 0.1 volt difference - switch the meters out and see if the difference is real, or in the meter calibration.

As far as if you wanted to get the voltages while the batteries are NOT connected in parallel -
It is pretty easy to measure them apart from each other - take the negative from the aux battery off the top of the ground cable that is on the IBS and measure that way. That should get a very real voltage of each battery when sitting in the garage not running.


Anyway, back on my other thoughts about the voltage differences, voltage drop, etc. - if my thinking is correct, there's more bad info out there than I first thought.
If I get caught up on other electric work, and things warm up a bit one of these days, I'll tear into mine and do some serious testing with things under load and settle it all in my mind once and for all.

My goal - add a couple of volt meters IN the cab of my truck, one for the crank, the other for the aux battery, so I can see the voltage of each and both at all times.

All the YouTube videos are for gas engines and it seems like a real PIA to pull the Aux battery if it is under the fuse box.

Pretty easy through the fender opening. In fact yet another forum member commented on how easy it was and in his thinking - it's the easiest way.

For the diesel, I can neither confirm nor deny the existence of the aux battery under the main battery.

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[steelponycowboy]

Well I can confirm that the Aux batter in the diesel is under the main batter. The fuse box on the diesel is moved to the front where the air cleaner is on the gas model. The air cleaner is moved to the drivers side front.

The diesel battery is moved against the fire wall and covers the Aux battery. I looked at the video of taking the Aux battery from the bottom and while it might look a bit easier, it still looks like a PIA.

In any case, I guess having a diesel makes it much easier to replace the Aux battery

 

[Gatorized]

Both of your meters are measure the combined voltage of the 2 batterries connected in parallel, just at different points in the circuit. You will have to seperate the batteries to get the individual battery voltage readings.

^^^
What Jerry said - however I find the differences shown in that pic interesting. I have always wanted to measure the VOLTAGE DROP across the wiring between the two batteries and through the PCR - and if you have two very accurate meters (which I suspect these are not necessarily) it would be only a 0.1 volt drop with no load.

I still think it's worth what you have done with those meters. What I'd do if it was mine since you are showing a 0.1 volt difference - switch the meters out and see if the difference is real, or in the meter calibration.

As far as if you wanted to get the voltages while the batteries are NOT connected in parallel -
It is pretty easy to measure them apart from each other - take the negative from the aux battery off the top of the ground cable that is on the IBS and measure that way. That should get a very real voltage of each battery when sitting in the garage not running.

Anyway, back on my other thoughts about the voltage differences, voltage drop, etc. - if my thinking is correct, there's more bad info out there than I first thought.
If I get caught up on other electric work, and things warm up a bit one of these days, I'll tear into mine and do some serious testing with things under load and settle it all in my mind once and for all.

My goal - add a couple of volt meters IN the cab of my truck, one for the crank, the other for the aux battery, so I can see the voltage of each and both at all times.

thanks for the input from you both - I know just enough to know there’s always more to learn! I thought the PCR was separating the batteries ,but clearly got the situation upside down since I know both batteries are charging when engine is off and a charger is attached to the crank battery positive and negative. Those readings were after my truck has been sitting for almost 3 weeks while on a charger to maintain SOC until I can drive again following hip replacement.
to get the actual readings for each, the Aux negative needs to be physically disconnected from the battery post (or I suppose, the Crank positive disconnected from N2). How do you separate them so you can have real time displays for both if it is not an auto stop event and the PDC has not powered the PCR to disconnect them?

 

[Mr._Bill]

thanks for the input from you both - I know just enough to know there’s always more to learn! I thought the PCR was separating the batteries ,but clearly got the situation upside down since I know both batteries are charging when engine is off and a charger is attached to the crank battery positive and negative. Those readings were after my truck has been sitting for almost 3 weeks while on a charger to maintain SOC until I can drive again following hip replacement.
to get the actual readings for each, the Aux negative needs to be physically disconnected from the battery post (or I suppose, the Crank positive disconnected from N2). How do you separate them so you can have real time displays for both if it is not an auto stop event and the PDC has not powered the PCR to disconnect them?

Use a normally closed relay and power it using an Aux switch. Put it in the negative line for the ESS battery. When the switch is off, the relay is closed, and the voltage reading is both batteries combined. When the switch is on, the relay is open, and the voltage reading is the single battery.

 

[Gatorized]

Use a normally closed relay and power it using an Aux switch. Put it in the negative line for the ESS battery. When the switch is off, the relay is closed, and the voltage reading is both batteries combined. When the switch is on, the relay is open, and the voltage reading is the single battery.

Something like this?
https://www.amazon.com/Continuous-A...locphy=9002492&hvtargid=pla-956964609503&th=1

 

[Mr._Bill]

Something like this?
https://www.amazon.com/Continuous-A...locphy=9002492&hvtargid=pla-956964609503&th=1

That should work. Disconnect the ESS battery negative cable from the main battery post and connect to one side of the normally closed path. Connect the negative side of the voltage meter in the same spot. Get a short cable to go from the other side of the normally closed path back to the main battery negative post. The two relay activation pins go to the Aux switch and ground. You will need to trace it out and make sure you get the correct negative cable coming from the ESS battery.

 

[jebiruph]

Here's a link to the battery monitoring discussion on the JL forum. https://www.jlwranglerforums.com/forum/threads/ess-dual-battery-management.60034/post-1287541

 

[Gatorized]

^^^
What Jerry said - however I find the differences shown in that pic interesting. I have always wanted to measure the VOLTAGE DROP across the wiring between the two batteries and through the PCR - and if you have two very accurate meters (which I suspect these are not necessarily) it would be only a 0.1 volt drop with no load.

I still think it's worth what you have done with those meters. What I'd do if it was mine since you are showing a 0.1 volt difference - switch the meters out and see if the difference is real, or in the meter calibration.

I did swap the meters and it seems to be a calibration issue. Interestingly enough, I disconnected the charger and an hour later the readings had increased to 12.8 for both.

 

[ShadowsPapa]

the readings had increased to 12.8 for both.

Perfect.

OK, so the difference followed the meters and not the batteries. That makes sense - they were the same, then. And that also makes sense.

 

[ShadowsPapa]

I need to post this in the "voltage" thread I have here I started almost a year ago - but interesting observations on my 2022 -
Drove from home to Overland Park, KS and back today. It's 220 miles, almost 3 1/2 hours.
Started out with a running voltage of 14.9. That lasted all the way down there.
Then coming back it started 14.8, then down to 14.7 and we stopped for gas a few minutes out of the KC area and it ran 13.0 the whole way home.
I need to check the battery voltages.
I don't know if part of the difference was we started out at sub-50 degree temps and in the 50s on the way back, or what.

 

[jebiruph]

I need to post this in the "voltage" thread I have here I started almost a year ago - but interesting observations on my 2022 -
Drove from home to Overland Park, KS and back today. It's 220 miles, almost 3 1/2 hours.
Started out with a running voltage of 14.9. That lasted all the way down there.
Then coming back it started 14.8, then down to 14.7 and we stopped for gas a few minutes out of the KC area and it ran 13.0 the whole way home.
I need to check the battery voltages.
I don't know if part of the difference was we started out at sub-50 degree temps and in the 50s on the way back, or what.

My experience has been that with a long drive that fully charges the batteries, the voltage still remains high until a power cycle (engine off/on). Then it goes back the regular variable voltage output.

 

[ShadowsPapa]

My experience has been that with a long drive that fully charges the batteries, the voltage still remains high until a power cycle (engine off/on). Then it goes back the regular variable voltage output.

The odd part is that we stopped at a rest stop between 2 1/2 and 3 hours in, and it was still 14.9 when we took off again. Then we finished the trip to our destination - still 14.9 when I stopped and still 14.9 when we took off again.
We had at least 3 stops after driving over 2.5 hours or more.
If nothing else it shows that you have to drive 4 hours or more to fully charge these as I've been driving this truck a lot lately.
Imagine - shoving 14.9, or even 15.0 volts at these for hours and still not fully charged.
I know the charge rate absolutely changes with temperatures - I've watched that happen, so it's really hard to say at what exact point it was temperature or what it was.

My 2020, you could see the voltage drop as you went. No stopping, it would start out about 14.6 or so, then slowly drop over time. On a long drive, like from CO back to Iowa, almost non-stop,. it went from 14 down to 12.6 as we drove.
So this one is very different from my 2020. I used to watch that one and know when things were getting charged up - I watched the voltage drop as I drove.

 

[BilletRUBI]

Just thought I'd share my experience...

I've had the Aux Switches message for a few months now. The last 3 weeks I could tell my engine wasn't turning over as fast as before, so I knew I was going to have to jump it at some point. Well, yesterday it wouldn't start.

I called the dealer and got in for a battery check. I jumped it using a battery booster without issue. Drove to the dealer 30 minutes away and they tested the batteries. Both were bad and they replaced them. The service manager said that both batteries usually run around $850 plus labor to install. Thankfully it was all covered under warranty!

 

[Jeepifer]

Just thought I'd share my experience...

I've had the Aux Switches message for a few months now. The last 3 weeks I could tell my engine wasn't turning over as fast as before, so I knew I was going to have to jump it at some point. Well, yesterday it wouldn't start.

I called the dealer and got in for a battery check. I jumped it using a battery booster without issue. Drove to the dealer 30 minutes away and they tested the batteries. Both were bad and they replaced them. The service manager said that both batteries usually run around $850 plus labor to install. Thankfully it was all covered under warranty!

I got the "truck will shut off" message today, what was your mileage and model year? My 2020 is 33k miles and curious if I should even bother with the dealer or do it myself

 

[ShadowsPapa]

I got the "truck will shut off" message today, what was your mileage and model year? My 2020 is 33k miles and curious if I should even bother with the dealer or do it myself

That's usually a very different animal, not a battery problem.
Batteries cause non-start or failure of ESS to operate. They don't cause it to say it will shut off.
Replacing batteries is extremely unlikely to fix your different problem.

Not starting != will shut off

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