Aux Battery Died, Weird Results When Doing Fuse 42 / Aux Battery Disconnection

[jebiruph]

The bit about it not starting after an ESS stop because of a blown N3 makes absolutely no sense to me.

Why? Because the aux battery is still connected to the electronics.
That aux battery is still powering the electronics. So that never changes no matter what.
Then -
All that the N3 fuse does is allow the aux to charge directly off the bus, and all the PCR does is take the aux off the bus so that only the main battery is running certain things.
For it to not start with a blown N3 - but moving that cable over to N4 and it starts?
No, doesn't make sense.
Think of those who replace batteries and blow the N3 leg of the high current fuse and drive not realizing it - until later. They are driving around, some even with a working ESS for a while until that aux battery goes down.

the only way it could maybe make a tiny bit is with a dead - very bad, main battery.
And then if the PCR closed and it tried to start - it might blow the N3 fuse. Cranking power would be coming from the aux battery through the N3 across the bus to the crank battery and starter.

But if that's the case, then moving the aux battery wire to N4 should blow the fuse again - because it's still trying to crank it to start through that fuse - but in that case, a restart, or cold start, which is much more power needy than an ESS restart.
Because the PCM has tracked things and kept all on the ready for that restart, it takes very little to start after an ESS stop compared to a big button start.
So if it's going to blow a fuse trying to start from an ESS stop, it's going to blow a fuse during a cold start when the starter is drawing more power for longer.

So to me, it still makes no sense.
ESS tries to restart, blows N3.
Move the wire over to N4, still only 150 amps, and use the big button to start it and it starts - not blowing the fuse this time?
Same set of circumstances except it takes more to start from the big button than an ESS start.

The difference between the cold start that doesn't blow the fuse and the ESS restart that does blow the fuse is for the ESS restart all the interior electronics are powered up. When the PCR reconnects the aux and main systems and the defective main can't power the starter, it's the additional surge of power from the interior electronics along with the aux battery power to the starter that is causing the N3 fuse to fail.

All of that to say this is the evidence that I've seen that the PCR reconnects the systems before restarting.

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[ShadowsPapa]

Except that during cranking, a lot of stuff actually shuts down and the electronics that are powered on already during an ESS stop and start don't go through any fuse - they are powered directly from the aux positive to N1, not through the fuse.
So those electronics that are "already on" don't go through the fuse.
The electronics go right to the aux positive, so there's no added load from them through N3.

Remember, those electronics, everything all still works with no N3 fuse because members have blown that fuse and driven away unaware. So the electronics don't go through N3 to create a load to blow it during an ESS start.

 

[jebiruph]

Except that during cranking, a lot of stuff actually shuts down and the electronics that are powered on already during an ESS stop and start don't go through any fuse - they are powered directly from the aux positive to N1, not through the fuse.
So those electronics that are "already on" don't go through the fuse.
The electronics go right to the aux positive, so there's no added load from them through N3.

Remember, those electronics, everything all still works with no N3 fuse because members have blown that fuse and driven away unaware. So the electronics don't go through N3 to create a load to blow it during an ESS start.

The electronics are the source, not the load. The fuse gets blown when the electrical energy in the electronics goes through the fuse on the way to the starter.

Having dual batteries alone can absorb spikes from restarting. The aux battery acts like a buffer protecting the electronics. So if the PCR closed first, you still have that small second battery taking the brunt of spikes ahead of the electronics.

What causes the spikes from restarting?

 

[foxwalkhq]

New battery came in. I disconnected both batteries and both were at decent voltages. ~11.5 volts.. I charged them both until the charger turned off. Main charged to 12.8 and aux I didn't check but once disconnected both batteries were ~12.5 volts.

I am basically waiting 45 minutes and will check their voltages.. What should I expect?

Is it possible that I just went too long without driving it?

I've been able to start it the past few days without jumping.

 

[Mr._Bill]

New battery came in. I disconnected both batteries and both were at decent voltages. ~11.5 volts.. I charged them both until the charger turned off. Main charged to 12.8 and aux I didn't check but once disconnected both batteries were ~12.5 volts.

I am basically waiting 45 minutes and will check their voltages.. What should I expect?

Is it possible that I just went too long without driving it?

I've been able to start it the past few days without jumping.

Fully charged, with no load, should read 12.8 volts after sitting for a while.

The parasitic draw is fairly high. It needs to have a battery maintainer connected if it is not driven regularly.

 

[foxwalkhq]

Fully charged, with no load, should read 12.8 volts after sitting for a while.

The parasitic draw is fairly high. It needs to have a battery maintainer connected if it is not driven regularly.

After sitting for 45 minutes after being fully charged Aux battery is at 12.11 volts and main battery is at 11.88 volts.

 

[Mr._Bill]

After sitting for 45 minutes after being fully charged Aux battery is at 12.11 volts and main battery is at 11.88 volts.

How old are the batteries? That much drop, after charging and with no load, indicates they both need replaced.

 

[foxwalkhq]

How old are the batteries? That much drop, after charging and with no load, indicates they both need replaced.

I bought the vehicle in September 2022 I believe.

 

[Mr._Bill]

I bought the vehicle in September 2022 I believe.

If you're willing to play dealer roulette, you can probably get them replaced. They are covered under the 3/36 warranty. It may be easier for you to just buy two new batteries and a maintainer.

 

[foxwalkhq]

If you're willing to play dealer roulette, you can probably get them replaced. They are covered under the 3/36 warranty. It may be easier for you to just buy two new batteries and a maintainer.

I hate going to the dealer. My USB ports cover was broke when I bought the vehicle. I had to leave it with them for 24 hours in order to do a job that would take me probably 2 hours.

As such I have changed the oil myself and not used the Jeep Wave.

I already bought the main battery so might as well just buy the aux.

 

[Mr._Bill]

I hate going to the dealer. My USB ports cover was broke when I bought the vehicle. I had to leave it with them for 24 hours in order to do a job that would take me probably 2 hours.

As such I have changed the oil myself and not used the Jeep Wave.

I already bought the main battery so might as well just buy the aux.

Be careful with the battery cables when swapping them. Completely disconnect the IBS from the negative post of the main battery so it resets. Fully charge the new batteries before installing them. I was able to turn the wheels full to the left and peel back the fender liner enough to get to the aux battery. Some prefer to remove the fuse box and go through the top.

 

[foxwalkhq]

Be careful with the battery cables when swapping them. Completely disconnect the IBS from the negative post of the main battery so it resets. Fully charge the new batteries before installing them. I was able to turn the wheels full to the left and peel back the fender liner enough to get to the aux battery. Some prefer to remove the fuse box and go through the top.

Removing the fuse box doesn't look like that big of a deal. More of an annoyance than anything else. I already watched a video of [Banned Site] do it on his JL Wrangler and took notes on it w/pictures.

BTW He didn't remove the IBS or anything.. all he did was disconnect the negative and positive leads from the main battery, then remove the aux battery and do the same.. put in the new aux, connect it, put in the new main, and connect it.

He didn't even disconnect either wire from the ground he just disconnected the entire - and + cables from the terminals leaving all other cables attached to them. Didn't seem to have a problem.

Is it really necessary to reconnect the IBS or reset it? or even fully charge them?

 

[sharpsicle]

Removing the fuse box doesn't look like that big of a deal. More of an annoyance than anything else. I already watched a video of [Banned Site] do it on his JL Wrangler and took notes on it w/pictures.

BTW He didn't remove the IBS or anything.. all he did was disconnect the negative and positive leads from the main battery, then remove the aux battery and do the same.. put in the new aux, connect it, put in the new main, and connect it.

He didn't even disconnect either wire from the ground he just disconnected the entire - and + cables from the terminals leaving all other cables attached to them. Didn't seem to have a problem.

Is it really necessary to reconnect the IBS or reset it? or even fully charge them?

Yes. Disconnect the IBS to ensure it resets. Just because someone else didn't do it doesn't mean it shouldn't be done. If I remember correctly, this is called out as necessary in Jeep's own procedure on battery replacement.

 

[foxwalkhq]

Yes. Disconnect the IBS to ensure it resets. Just because someone else didn't do it doesn't mean it shouldn't be done. If I remember correctly, this is called out as necessary in Jeep's own procedure on battery replacement.

How long does it take for the IBS to reset once unplugged?

 

[sharpsicle]

How long does it take for the IBS to reset once unplugged?

Supposed to be 10-15 minutes. I'd let it sit 30 minutes to be safe/sure.

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