Driving without an aux battery

[J0E]

Why don’t you just fix it? Takes very little time and effort.

Why would you want one? Just pull F-42 and negative and disable ESS.

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[Reinen]

Here's why you always replace both Main and Aux at the same time.

• Batteries do not flip between good/bad like a light switch. They slowly and progressively become worse. When a battery tests "bad" it's just an arbitrary point when the battery should be replaced. Conversely, when a battery tests "good" it can still be much closer to "bad" than "new".
• On a JL, the Main and Aux batteries are linked 99.9% of the time. If you only replace one, the older battery will be like a vampire to the new battery. The new battery will try to equalize with the older battery 24/7, which isn't possible because the older battery is more worn out. This ends up sucking the life out of the new battery until it's just as worn out as the older battery.
• You can change only one battery at a time but in the long run you will go through much more batteries than if you replace both Main & Aux at the same time so they are both equally new.

You can bypass the Aux battery as others have linked. But this has one big downside. When your main battery inevitably fails you will have no warning and can be left stranded. With the Main/Aux design, the first thing that will fail is ESS. The rest of the JL will still function. This is a 2-3 month warning before you have strange electrical issues and can find yourself stranded. A clear signal that it's time to replace both Main and Aux while still being able to drive the Jeep.

 

[Jeep4Win]

Shouldn’t it be an aux14? The dealer replaced it under warranty years ago.

They come with a 14. If you go to an Autoparts store just tell them you want a 14. I wouldn’t bother giving them your make and model because it will tell them to sell you a 12.

 

[J0E]

Here's why you always replace both Main and Aux at the same time.

• Batteries do not flip between good/bad like a light switch. They slowly and progressively become worse. When a battery tests "bad" it's just an arbitrary point when the battery should be replaced. Conversely, when a battery tests "good" it can still be much closer to "bad" than "new".
• On a JL, the Main and Aux batteries are linked 99.9% of the time. If you only replace one, the older battery will be like a vampire to the new battery. The new battery will try to equalize with the older battery 24/7, which isn't possible because the older battery is more worn out. This ends up sucking the life out of the new battery until it's just as worn out as the older battery.
• You can change only one battery at a time but in the long run you will go through much more batteries than if you replace both Main & Aux at the same time so they are both equally new.

You can bypass the Aux battery as others have linked. But this has one big downside. When your main battery inevitably fails you will have no warning and can be left stranded. With the Main/Aux design, the first thing that will fail is ESS. The rest of the JL will still function. This is a 2-3 month warning before you have strange electrical issues and can find yourself stranded. A clear signal that it's time to replace both Main and Aux while still being able to drive the Jeep.

Agree with matched set of batteries. That's why when I build inverter systems and use a 24 V inverter I put the batteries in series so you don't have the problem of lowest voltage equilibrium.

But that's nonsense paying for ESS so you might be warned and never need to test your battery or know it's condition. Battery testers are cheap. You're just about as likely to have the primary or both fail.

 

[Reinen]

Agree with matched set of batteries. That's why when I build inverter systems and use a 24 V inverter I put the batteries in series so you don't have the problem of lowest voltage equilibrium.

But that's nonsense paying for ESS so you might be warned and never need to test your battery or know it's condition. Battery testers are cheap. You're just about as likely to have the primary or both fail.

Not paying for ESS isn't an option, thanks to our government. Battery testers are cheap but the reality check is that it requires OCD to use it pretty much every time you drive.

So since you have to pay for it you might as well use it's most useful feature. The battery check.

The gas savings is just an okay, maybe it saves a smidge, whatever thing.

 

[multicam]

Not paying for ESS isn't an option, thanks to our government. Battery testers are cheap but the reality check is that it requires OCD to use it pretty much every time you drive.

So since you have to pay for it you might as well use it's most useful feature. The battery check.

The gas savings is just an okay, maybe it saves a smidge, whatever thing.

If you leave your Aux battery installed (but disconnected), it could serve as a jumping battery in a pinch. Just reconnect the negative and fuse 42. Although I’m not sure how long it would take for it to just die if it’s disconnected and never used.

 

[Reinen]

If you leave your Aux battery installed (but disconnected), it could serve as a jumping battery in a pinch. Just reconnect the negative and fuse 42. Although I’m not sure how long it would take for it to just die if it’s disconnected and never used.

AGM batteries self discharge 2-5% per month depending on the battery (newer ones are better). But jump starting isn't the big concern. It's when a battery fails and can no longer supply enough power to keep the electronics happy even with the engine running. The JL doesn't like that at all, unlike older vehicles where starting the engine was the only real hurdle.

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