Service Stop/Start System Message and Warning

[Thor64]

Well after an overnight charge of the main battery with aux batt isolated and PCR fuse pulled—no more service ESS. Hopefully the main has not been degraded too much by the auxiliary. Thanks everyone for the educational information!!

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[AndySpill]

The JL was designed with two batteries because Jeep owners expect to be able to install aftermarket electrical accessories directly to the Main battery. It's a very common practice. Instead of putting limits on that practice, Stellantis engineers opted to protect the power-sensitive JL electronics from this unknown owner-installed power demand by powering the electronics with an 2nd Aux battery that is isolated from these modifications during ESS events.

Other auto makers have the luxury of assuming the owner will not alter the OEM electrical system as it's a fairly uncommon thing to do. They will also be very quick to blame any failure on the owner-installed modification. Jeep customers do not allow such a luxury.

It's ironic. Jeep's customers love to complain about the Aux battery when the only reason why it exists is because of Jeep's customers. Engineers can't win for losing.



#1 reason is that it also deletes a degree of reliability and ability to perform preventative maintenance before failure. A Jeep is a vehicle where you cannot assume Roadside Assistance is available or even cell service.

With Aux Batt/ESS as designed, every time ESS engages confirms a successful battery check. It would take beyond OCD-level maintenance to check the batteries more often. In the event of battery failure the first thing to fail is ESS. As you well know, nobody cares if ESS fails. But it does give you a 2-3 month warning that a critical battery failure will occur that will leave you stranded. More than enough time to perform preventative maintenance. It's a very valuable "canary in the coal mine".

With Aux Delete/ESS Disabled, your first sign of battery failure (which is inevitable) will very likely be a critical failure that leaves you stranded, unable to start the vehicle. For someone like me, who owns a JL specifically to go deep into areas with no infrastructure, no roadside assistance and no cell service this is utterly unacceptable. It will very likely lead to an extremely inconvenient and potentially life threatening situation. Even if you always stay in civilization, why would you delete a very convenient passive warning that allows you to replace your failing batteries at your convenience? Ain't nobody got time for dead transportation. I don't understand the mentality behind it.



Welcome to the genius behind Washington DC. It doesn't make much sense but vehicle manufacturers have no choice, it's a must-have "feature" now. At least Jeep had the wherewithal to turn it into a 2-3 month battery failure warning. Now that is a valuable feature that few other vehicles have.

Thank you for your thoughts.

Perhaps I have missed the gist of it or not covered its thoughts adequately, but if I were to summarize it I'd be inclined to say that "@Reinen's point is in that the presence of the ESS battery, and in the running of ESS events it is based on, we are benefiting from a "canary in the mines" advance warning of main battery's demise that we can preventatively address when expediently convenient rather than 'on Route 75 in Florida's alligator alley.' "

Ok, but the fly in that ointment, as I see it, if I even have you right is that:

1) For many a dual AGM battery JL owner, particularly your short infrequent trip user who doesn't trickle charge, the connection of that battery catalyzes the very demise of that main battery whose advance warning of that demise you seek to detect, and

2) With the Aux battery and Fuse 42 disconnection the owner is still free to on occasion invoke ESS events where the battery test you reference will be done on the one main battery.

(I have no horse in this race trying to get people to justify my one battery decision by acting in kind. I run both batteries, ESS events, and trickle charge, effectively, if even indirectly, following your "canary in the mines" advice.)

 

[Reinen]

Thank you for your thoughts.

Perhaps I have missed the gist of it or not covered its thoughts adequately, but if I were to summarize it I'd be inclined to say that "@Reinen's point is in that the presence of the ESS battery, and in the running of ESS events it is based on, we are benefiting from a "canary in the mines" advance warning of main battery's demise that we can preventatively address when expediently convenient rather than 'on Route 75 in Florida's alligator alley.' "

Ok, but the fly in that ointment, as I see it, if I even have you right is that:

1) For many a dual AGM battery JL owner, particularly your short infrequent trip user who doesn't trickle charge, the connection of that battery catalyzes the very demise of that main battery whose advance warning of that demise you seek to detect, and

2) With the Aux battery and Fuse 42 disconnection the owner is still free to on occasion invoke ESS events where the battery test you reference will be done on the one main battery.

(I have no horse in this race trying to get people to justify my one battery decision by acting in kind. I run both batteries, ESS events, and trickle charge, effectively, if even indirectly, following your "canary in the mines" advice.)

Well, you're making a statement in point 1 but not providing any reason why the statement is true. Why is the Aux battery catalyzing the demise of the main? It could just as easily be the Main catalyzing the demise of the Aux. It is true that in a parallel two battery system, the lifespan of both batteries will be the shortest lifespan of the two batteries. The more degraded battery will degrade the other until they're both equally degraded, but relatively speaking that's only a minor downside with two new batteries. It only becomes a severe problem when you replace one battery at a time. That will quickly destroy the new battery until it's just as degraded as the older battery. To maximize lifespan both batteries need to have the same age and use from day 1 (i.e. both new and put into service at the same time).

In point 2, yes this is true but now you don't have Aux assisting the main in any way. That adds an additional 20% or so burden to Main during cold starts which impacts the ESS battery test. During ESS warm starts the electronics that manages the start can now be impacted by the demand of the starter motor. Having just enough power to crank the starter becomes moot if it also browns out the electronics and the engine start can't be managed properly.

The reason why the Aux battery delete persists is because it works, at first. Where it's worse is at the end of the battery lifecycle which will come sooner and is more likely to be a critical failure.

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