Main vs Aux battery replacement question on 2021 JT

[Mojave2021]

Hi - I bought my 2021 JT in May 2021 and still have the original main battery running. The original aux battery was replaced in mid August 2022.

The JT has 15K miles now and has the "Auxiliary switches aren't available" message every time I start it cold in the morning. I don't think the start/stop has been working for months now either though I don't have any Service ESS errors on it like I did when the original aux battery crapped out on me.

Do you guys think I should replace both batteries at the same time, or just replace the main battery (I'm assuming it's due for replacement).

Thanks

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[ShadowsPapa]

Hi - I bought my 2021 JT in May 2021 and still have the original main battery running. The original aux battery was replaced in mid August 2022.

The JT has 15K miles now and has the "Auxiliary switches aren't available" message every time I start it cold in the morning. I don't think the start/stop has been working for months now either though I don't have any Service ESS errors on it like I did when the original aux battery crapped out on me.

Do you guys think I should replace both batteries at the same time, or just replace the main battery (I'm assuming it's due for replacement).

Thanks

IDEALLY, both. But - as long as the aux battery is still good, do the main if you wish or can't afford both.

The lack of ESS working and the "auxiliary switches unavailable" message is simply a low battery voltage indication. We get that one our 4xe if it sits a long time - and it doesn't even have an aux battery. So it just means low battery voltage, and that could be the main.

Always charge new batteries before installing and reset the IBS ->

 

[MattK]

In my experience and help from the forum heroes is to replace them both at the same time and follow some simple steps to ensure they are fully charged before you drop them in as well as reset the Intelligent Battery Sensor (IBS).

 

[Mojave2021]

Thanks guys for the quick responses!

 

[MudderNuker]

Both. In case your JT turns into a Christmas tree with all kinds of lights flashing and a transmission message (happened to me twice, one after attempting to remote start), if you disconnect the first cable closer to the front of the vehicle going into the fuse box for a few seconds, the errors will go away and you should be able to jump start the vehicle.

 

[ShadowsPapa]

Both. In case your JT turns into a Christmas tree with all kinds of lights flashing and a transmission message (happened to me twice, one after attempting to remote start), if you disconnect the first cable closer to the front of the vehicle going into the fuse box for a few seconds, the errors will go away and you should be able to jump start the vehicle.

That's N1 and it's where the "system's electronics" connect. So pulling that cable, you are effectively shutting off power to all of the electronics, each module, of the vehicle, forcing a reset of sorts.

 

[MudderNuker]

That's N1 and it's where the "system's electronics" connect. So pulling that cable, you are effectively shutting off power to all of the electronics, each module, of the vehicle, forcing a reset of sorts.

I had forgotten the nomenclature of that particular connecting post. Thanks.

 

[ShadowsPapa]

I had forgotten the nomenclature of that particular connecting post. Thanks.

IMO, it's also easier than pulling battery cables, and separating them........

 

[Mojave2021]

It’s been a while since I posted this but I still haven’t replaced the batteries. Today I stumbled on this YouTube video to disconnect the sensor and connect it again. My stop/start is working for the first time I think in 3 years. It did take it one drive to wake up again after reconnecting.

Going to hold off on replacing the batteries for now. My voltage looks good at 14.4 too.

 

[ShadowsPapa]

Going to hold off on replacing the batteries for now. My voltage looks good at 14.4 too.

That's not an indication of "good" - it simply means it senses the batteries are low and need to be charged. It's not battery voltage.

You either need to charge them, drive it more - or watch that voltage as if it stays there, they aren't getting charged enough, or aren't taking a good charge.
If the batteries were 100% charged, you'd soon see voltage in the 13s.

 

[Mojave2021]

Ok but the voltage on the dash I thought was normal - it’s between 14.2 and 14.4 most of the time. But I had thought I had battery issues since the stop start was never ready. We’ll see if it keeps working.

The aux buttons sometimes still show as unavailable if I haven’t started it for a few days but quickly become available. My understanding is that’s normal too.

 

[Thunderspud]

it’s between 14.2 and 14.4 most of the time.

I think the idea is that if you are seeing those on the dash it would indicate the truck is attempting to charge the battery (or batteries) all the time. It would not be doing this if the truck thought they were already fully charged,

 

[ShadowsPapa]

Ok but the voltage on the dash I thought was normal - it’s between 14.2 and 14.4 most of the time. But I had thought I had battery issues since the stop start was never ready. We’ll see if it keeps working.

The aux buttons sometimes still show as unavailable if I haven’t started it for a few days but quickly become available. My understanding is that’s normal too.

That's not normal - unless the batteries are getting weak and not holding a charge, or, you aren't driving it enough to keep them charged.

When the batteries are up, you'll see in the 13s. On a long drive, where the batteries get totally charged, you might see the voltage drop below 13.
If mine sits 2 or 3 days it will be in the 14s until I've driven it about an hour total, then it will drop back.

You might see from 12.6 up to 15, depending on the battery state of charge, air temperature, and other factors.

 

[Mojave2021]

I had been out of town and not driven it in a week before messing with the sensor.

Tonight driving around town it was at 13.7 most of the time. Stop / start continued to work perfectly. I’ll have to see if that reset helps avoid the aux button warning - haven’t had a chance to test that since reconnecting the sensor.

 

[ShadowsPapa]

I know youtube is the training college for a lot of people - but half of the stuff out there is just shadetree or hack stuff that people figured "hey, I did this and that happened" - never understanding the why or how, and it's only half the story, or not really the best way to do things.

Ideally, even according to documents, you do the IBS reset with fully charged batteries.
Resetting the IBS doesn't really necessarily fix anything.
It will force it to LEARN the battery state, health and state of charge and can sync things back up again.
But - it's normally done on fully charged batteries (meaning using a battery charger, not driving to charge)

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