Jumperless Aux Battery Bypass

[Ratbert]

Absolutely fantastic write up on the ESS stuff @Jebiruph I've been following this with intrigue and while I had a Wrangler (well 2 4xes) I"ve never owned a ESS dual battery equipped vehicle. I do now however have a 23 Grand Cherokee Laredo with the dual battery ESS system.

The whole premise and function is the same as you have outlined obviously the wiring and schematics are a bit different.

Here is my question about bypassing the Aux battery in the least invasive way possible.

I've always had a fascination with Lithium batteries and was thinking about installed a lithium battery to replace the Aux 14 battery. (I already have a large automotive grade lithium battery)

However that won't just work because its resting voltage is higher and will drain itself completely trying to charge the main battery while the vehicle is off. It would however work as a back up to jumpstart the main battery if needed.

So my question is this.

Can one simply pull the F42 fuse (which I haven't figured out which one it is in the WL Grand Cherokee) and then instead of disconnecting the negative cable on the aux, simply wire a battery disconnect switch?

I've seen your previous posts about wiring a disconnect with gauges ect.....not looking for something that elaborate (it really isn't but I don't need to monitor the battery as it's got built in monitoring)

Thanks for your time and all the work involved with this ESS system.

Interesting idea, but you've got me wondering about putting a standard LiFePO4 battery in there with a DC to DC converter and powering a fridge, etc. from it. I'm guessing that it'd be a pretty wimpy battery though.

Sponsored

 

[Tyler-98-W68]

Interesting idea, but you've got me wondering about putting a standard LiFePO4 battery in there with a DC to DC converter and powering a fridge, etc. from it. I'm guessing that it'd be a pretty wimpy battery though.

I have quite a bit of experience with Lithium batteries so I can explain why it would and wouldn't work.

If you are wanting to have a lithium ESS battery in place of the stock AGM and have it connected to the main battery it won't work well at all.

Lithium batteries rest at a higher voltage (around 13.4v) and only rest around 12.8v (like an AGM) when they are almost completely discharged. What that means is that when connected (which is most of the time in an ESS system) the lithium battery will discharge and try to charge the AGM battery.

The next part is charging, you can get automotive lithium batteries that work fine in conventional alternators, the issue in this example is the battery is only 13ah, and generally you don't want to charge lithium at much more than 0.25c (or 25% of its rated capacity) in this case around 3amps, the stock charging system will put out far more than that.

Now if you want to do this with the battery separated like the point of this thread with a DC/DC charger that would absolutely work, The issue is going to be how small the location is for the battery is not going to give you much in terms of capacity.

 

[Ratbert]

I have quite a bit of experience with Lithium batteries so I can explain why it would and wouldn't work.

If you are wanting to have a lithium ESS battery in place of the stock AGM and have it connected to the main battery it won't work well at all.

Lithium batteries rest at a higher voltage (around 13.4v) and only rest around 12.8v (like an AGM) when they are almost completely discharged. What that means is that when connected (which is most of the time in an ESS system) the lithium battery will discharge and try to charge the AGM battery.

The next part is charging, you can get automotive lithium batteries that work fine in conventional alternators, the issue in this example is the battery is only 13ah, and generally you don't want to charge lithium at much more than 0.25c (or 25% of its rated capacity) in this case around 3amps, the stock charging system will put out far more than that.

Now if you want to do this with the battery separated like the point of this thread with a DC/DC charger that would absolutely work, The issue is going to be how small the location is for the battery is not going to give you much in terms of capacity.

Yeah, I explicitly stated that it'd be with a DC to DC converter. That mitigates just about everything that you said. The only concern would be that it'd be pretty damn small. Again: as I stated.

I only found one candidate and it's a puny 4AH: https://www.batteriesplus.com/product-details/powersports/battery/x2power/cyl10088. So no, it doesn't make sense.

 

[Acme]

Hello. I'm trying to unplug my aux battery. I removed the F42 fuse. But unless I keep the 2 negative wires connected to the main battery, my Jeep won't turn on. Any idea? I don't understand, based on all my readings, this shouldn't happen.

 

[ConqSoft]

Hello. I'm trying to unplug my aux battery. I removed the F42 fuse. But unless I keep the 2 negative wires connected to the main battery, my Jeep won't turn on. Any idea? I don't understand, based on all my readings, this shouldn't happen.

You only disconnect the one that goes to the AUX battery. If you remove one and the Jeep doesn't start, try reconnecting that one and disconnect the other one.

 

[Acme]

You only disconnect the one that goes to the AUX battery. If you remove one and the Jeep doesn't start, try reconnecting that one and disconnect the other one.

Yeah, I tried both. And the Jeep doesn't turn on (dash is completely dead) unless I connect both. That's the part I don't understand... I just bought a new main battery and I want to make sure the aux battery isn't going to drain it, but I'm very confused... how it's possible that I need to have both wires connected to have power. It makes no sense based on the wiring schemas. ?

 

[azjl#3]

While I was stuck changing a bad battery in the autozone parking lot, besides the fuse trick, you can fit a larger battery into the jeep battery tray. There is a plastic "filler" on forward side of battery tray, remove that, and you can put a larger/ more A/H battery, in place. Sorry, can't remember what size I bumped it up to. But 850cca now vs 700 something

 

[Heimkehr]

I just bought a new main battery and I want to make sure the aux battery isn't going to drain it, but I'm very confused... how it's possible that I need to have both wires connected to have power. It makes no sense based on the wiring schemas.

Just thinking out loud here:
Does the rectangular sensor (on which the screwdriver tip is resting) maintain a connection to the negative post when you attempt to remove/isolate the cable specific to the small ESS battery?

 

[Acme]

Just thinking out loud here:
Does the rectangular sensor (on which the screwdriver tip is resting) maintain a connection to the negative post when you attempt to remove/isolate the cable specific to the small ESS battery?

Things need to be done in a certain order. I think the problem was indeed the sensor. When you do things "out of order" the sensor cuts the connection. I think... Now it's working as expected. I'm not sure what I did wrong the 1st time.

 

[Tejas]

Had both batteries replaced 1 year ago under warranty. I got the Aux switches message the other day and Jeep was dead the morning. Sad state of affairs when OEM aux battery only last 12 months. Pulling the fuse, disconnecting the small ground and replacing the main with an Optima H7.

 

[Heimkehr]

Had both batteries replaced 1 year ago under warranty. I got the Aux switches message the other day and Jeep was dead the morning. Sad state of affairs when OEM aux battery only last 12 months.

Possibly there's a parasitic draw causing abbreviated battery life. I say this primarily in the context of the recent, warranty-based replacement of also-young batteries.

 

[Dale's Jeep]

Dumb question but if you pull fuse and remove negative battery cable. Why can't you remove aux battery wiring harness completely?

 

[andy29847]

Dumb question but if you pull fuse and remove negative battery cable. Why can't you remove aux battery wiring harness completely?

You can remove the aux battery and wiring. You will need a connection between N1 and N3.

 

[Blue Bear]

I was going to pull fuse 42 and disconnect the aux battery terminal on my '23 JLUR yesterday, but low and behold, the aux and main terminals are one piece! I'm not too keen on cutting them apart. Anything else I can do? I've already blown though an aux and main battery, and now I'm constantly waiting for the next shoe (battery) to drop. :| Eventually, I think I'm gonna pull the trigger on a Genesis system, but I just don't wanna spend that kinda cash anytime soon.

 

[jludave]

the aux and main terminals are one piece!

Please post a pic. I believe you are the first to report this.

Sponsored