What’s the JL’s main battery good for?

[Phyz]

So the V6 models use two batteries. What happens if you disconnect the small battery? What if you disconnect the big battery? The results are ... non-intuitive.

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[sigsegv]

It's possible I am completely confused, but from what I see at 3:15 () he puts the voltmeter across the small battery and it reads 11.6 volts.

Edit: that's the voltage of his little battery. Is it dead? It's a lead acid battery, right? That seems really low.

At the beginning of the video he has a voltmeter across the main battery after disconnecting the ESS battery, and it reads 12.5 volts.

 

[RonAZ]

Big battery must just be for the winch. Now you can run main battery down and still start jeep. Might be giving the engineers too much credit though.
I see small caps on the little battery. Sure hope you don't have to add water.

 

[Pipebndr]

Reading what I can from bits and pieces of the wiring diagrams posted, is the aux battery is used to control relays that control the power drawn off the primary battery. Without the aux battery the controls won’t activate the relays to utilize the main battery. This is why disconnecting the aux battery kills the system. Using a lower amperage circuit to ignite a relay for a heavier load, this keeps small switch’s from handling large amperages and burning up.

 

[Venosiar]

I was gonna go optima https://10carbest.com/best-jeep-battery But they recenty moved to Mexico and the quality has gone down hill significantly. (according to fellow jeepers and the battery stores here) so I went with odyssey. It was $275 it has lifetime to questions asked full replacement on it. But I think that was just the store here that did that for me

 

[marjamr]

So this doesn’t really answer the question as far as I can tell.
With rhe small battery disconnected the big battery will power all the accessories, radio, guages, windows etc. But, the jeep wont start. With the small battery conected but not the big battery, the jeep will start and it looks like the electronics conecon too. Lights, guages etc.
so, what is the purpose of the big battery?

 

[Jebiruph]

So this doesn’t really answer the question as far as I can tell.
With rhe small battery disconnected the big battery will power all the accessories, radio, guages, windows etc. But, the jeep wont start. With the small battery conected but not the big battery, the jeep will start and it looks like the electronics conecon too. Lights, guages etc.
so, what is the purpose of the big battery?

The big battery powers the starter for all starts along with powering everything else except when auto stopped, then some of the electronics are powered by the small battery. I do not know why things act the way they do when the individual batteries are disconnected.

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