Small Auxiliary Battery With ESS?

BillyHW

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Hey folks,

I was going over some specifications for the 2017 Jeep Grand Cherokee and 2017 Chrysler Pacifica (non-hybrid) and there appears to be a smaller auxiliary battery in them.

This smaller auxiliary battery does not appear to exist in other FCA vehicles with ESS like the regular Cherokee.

Does anyone know if this smaller battery is used directly to restart the engine during an ESS cycle, or is it somehow used for interior electrics while the engine is turned off during ESS? How is it used and how does it interact with the main battery?

Does anyone know if the 2018 Pentastar JL will have this auxiliary battery? I don't remember reading anything about it in the leaked owner's manual.

Here is a video that shows the smaller auxiliary battery along with the big main battery:

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Grimmjpr

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From what I can tell on my Grand Cherokee the small battery just adds a bit of CCA to the standard battery. It looks like they both supply power to the all vehicle systems. I'd guess instead of having extra part numbers for batteries in all trims they can just add the small battery to the ESS vehicles that they deem it necessary to put it in. I like having a little extra battery capacity since I have an ARB fridge I run on trips.
 
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BillyHW

BillyHW

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Hey folks, looks like the 2018 3.6L has the same ESS "dual battery" system as the current GC I posted a video above. Confirmed from the configurator output:

Screen Shot 2017-12-20 at 6.27.30 PM.png


I think it's just to keep the cabin equipment like radio and A/C running during an engine stop event, leaving the main battery just for restarting the engine. They are both 12V but the main one is big and the auxiliary is small.

This is not the same thing as eTorque.
 
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BillyHW

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Does the 2nd battery keep the ECU powered when the main battery is disconnected?
My guess would be no, but why would the main battery be disconnected?
 

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I was told by the dealer it only is used for the ESS starts. When I was complaining about that stupid system I was complaining that it had to take its toll on the battery always restarting like that. That is when he said they have a cheaper, smaller battery just for that job. Take it for what that is worth. BTW talking about a 17 Jeep GC
 

Grimmjpr

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That small battery is about 135CCA not sure it would be able to start the engine over and over again without the help of the larger battery. My ARB fridge is wired directly to the battery in my Grand Cherokee, both batteries are attached to the same positive and negative leads best I can tell when I tested the voltage from ground to either battery positive, or primary battery positive to aux battery negative at the wiring harness or vice versa I got the same voltage indicating that they are linked together. The configuration in the JL could be different but in the Grand Cherokee both batteries appear to feed everything together.
 
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BillyHW

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Pretty sure the main, larger battery is used for the engine starts and the smaller one is used to keep the cabin equipment operating seamlessly while the engine is stopped and starting.

But of course I don't know for sure.
 

TIDALWAVE

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Grmmjpr: Does that mean that the smaller ESS auxiliary battery could be used as the second battery for a camping overlanding run?
I plan on camping with a ARB fridge but don't want to drain the main/starting battery if the JL sits for a day or two. The typical two battery setup generally runs about $1K. I only want to pull a small amount of current to run the fridge. So is the ESS battery relay-separated from the starting battery when the engine is shut off?
 
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BillyHW

BillyHW

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Grmmjpr: Does that mean that the smaller ESS auxiliary battery could be used as the second battery for a camping overlanding run?
I plan on camping with a ARB fridge but don't want to drain the main/starting battery if the JL sits for a day or two. The typical two battery setup generally runs about $1K. I only want to pull a small amount of current to run the fridge. So is the ESS battery relay-separated from the starting battery when the engine is shut off?
The aux battery looks way too small to be useful for camping, unfortunately.
 

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Any idea where the ESS auxiliary battery is located?
 

TIDALWAVE

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I was hoping that 1) it was relay-controlled similar to a dual camping set up and 2) that is was located in a convenient enough spot such as in the cabin...so that a third battery of sufficient capacity could be installed to be a true camping battery. But without the hundreds of dollars an add-on dual battery system typically costs.
I installed an inverter on my JK...now the Rubicons come standard with an inverter.

Update: discussing this with a friend...the ESS battery HAS to be relayed to the starting system. If both batteries were simply parallel wired..the two would combine a single larger storage capacity and it would be much cheaper to have a larger capacity main battery than adding the extra wiring and ESS battery.

The main battery has been moved forward in the engine compartment. Switched places with the fuse/power box. Wonder if there will be enough room at that location to install two batteries?.
 
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BillyHW

BillyHW

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I was hoping that 1) it was relay-controlled similar to a dual camping set up and 2) that is was located in a convenient enough spot such as in the cabin...so that a third battery of sufficient capacity could be installed to be a true camping battery. But without the hundreds of dollars an add-on dual battery system typically costs.
I installed an inverter on my JK...now the Rubicons come standard with an inverter.
Interesting idea. I guess will have to wait and see if there's any extra space for a third battery. Or maybe enough space to swap out the small one for a big one?
 

Grimmjpr

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Grmmjpr: Does that mean that the smaller ESS auxiliary battery could be used as the second battery for a camping overlanding run?
I plan on camping with a ARB fridge but don't want to drain the main/starting battery if the JL sits for a day or two. The typical two battery setup generally runs about $1K. I only want to pull a small amount of current to run the fridge. So is the ESS battery relay-separated from the starting battery when the engine is shut off?
Sorry for the delayed response, I've been traveling for work. No the auxiliary battery is small so it's really not like a dual battery set up and wired to the main battery, at least in my Grand Cherokee anyway. That being said I've run my ARB fridge for 2 to 3 nights without starting the Jeep. I carry a jump starter pack in case but the fridge pulls about 1 amp hour average so your pretty safe going 2 nights. If I'm not mistaken the battery in the Grand is 80 amp hours and the battery in my Wranglers were 70. HTH
 
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