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Relocating and Upgrading Aux Battery?

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MrWaxman

MrWaxman

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I believe your above statement is correct. But, the same would happen if the 2 batteries are the same size, except we'd expect a longer life on the (now larger, same size) aux battery.

If you're already repositioning it to an easier to access location, it might be easier and cheaper to use a smaller battery, replacing it more frequently. Or you could use a bigger battery, replacing it less frequently.
I think you are correct after considering your input. I appreciate it a lot.
 

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Yeah, same size and same life expectancy is probably best, meaning start fresh with two new batteries, just as you would if you had to replace either the main or aux normally.

TJ: What I'm getting is that you might separate the batteries with the engine off. Run your gear and then reconnect them just prior to re-cranking for the ride home?
 

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I'm not exactly sure what the smaller battery in the Ecodiesel does different than in the 3.6L.
It does, however, seem to me that the #1 problem across any model Wrangler with the dual battery system is the dual battery system.
I think relocating a part of a very common problem instead of eliminating the (2nd battery) problem altogether is a lot of effort and little ROI.
 

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Hot Rodders have been relocating batteries to the trunk for decades. It's not a big deal. Find some old welding leads at a construction type company and run them protected in PVC along the frame. Could even modify the hidden storage box in the rear to house the batteries below the deck. Dang, i'm talking myself into it.
 

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What are the physics of dissimilar size batteries causing battery wear?
The science for not paralleling non-identical batteries is based upon charging such a system. Due to AGM engineering and lead-acid chemistry, prompt and accurate charging (along with discharge limits) is essential for maintaining battery bank performance over time. Charging is governed by Ohm's Law, which explains why non-identical batteries in a single bank system will experience unnecessary electro-chemical damage (likely non-identically).

A system which has non-identical batteries needs non-identical charging for each battery, which is not provided in stock Wranglers.
 

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And, I believe the trailer harness wires are each fused at 30 amps or less.
So I'm clear, and probably wasn't, I'm suggesting that this below the cabin route might also be one, albeit for considerably thicker (lower gauge) cable that might connect a larger Aux battery in the cargo area with that which goes on under the hood.

I admit to not having a handle on "ampacity hits" that such a distance, or potential exposure to cold weather (not cable physical exposure: which should have protective housing) might experience.
 

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Why bother there is no need for two 12v batteries. One robust 12v main battery is all that is needed. Even the stock main 12v battery is adequate. Just disconnect the tiny 12v battery.
I got the sense from the OP Paul, maybe wrong, that this larger Aux battery would be one that might serve appliances as a disconnected one (unlike factory setup) from the main battery when the engine is off and such power is desired, with its role as an ESS battery being only, at best, some other need the battery might serve.
 

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I don't understand your desire to remove this auxiliary battery. The original batteries are AGM technology and quality. I have a few friends who have Wrangler JLs equipped, and haven't had a problem for 4 years. I myself have just changed the auxiliary after 5 and a half years for 55 euros (dollars) and the ESS is working normally again. the main one can still work for 2 years. Why keep it simple when you want to make it complicated...
 

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AndySpill

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I don't understand your desire to remove this auxiliary battery. The original batteries are AGM technology and quality. I have a few friends who have Wrangler JLs equipped, and haven't had a problem for 4 years. I myself have just changed the auxiliary after 5 and a half years for 55 euros (dollars) and the ESS is working normally again. the main one can still work for 2 years. Why keep it simple when you want to make it complicated...
The desire to remove the auxiliary battery comes from people's desire to not run the ESS system, resulting in little upside to keeping the ESS/Aux battery within the electrical schematic of the vehicle: a battery that for more than a fair number of owners has proved problematic and cannibalistic on the main battery in part due to the very size difference it bears with the main battery, which it is connected to in parallel 99.9% of the time in the factory based wiring.

People in large part are also not physically removing this battery. They're merely breaking electrical connection to it by disconnecting the black cable that leads from its negative post to the negative post of the main battery, insulating this loose cable end, turning off the ESS system, and yanking fuse 42 in the Power Distribution Center (PDC) to prevent the Power Control Relay (PCR) from ever being energized and breaking the factory connection between the two batteries at cold cranks and ESS events, so that calls for isolated power from the now disconnected ESS/Aux battery get routed to all batteries, of which only one remains: the main battery.

Your batteries' longevity and your approach to simply change one, not both the them, sadly does not conflate with the experience of many dual AGM battery owners.
 
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Being that you have the diesel and your aux is accessed through a door/panel under the main, making it the easiest aux battery access/change, I just wouldn't worry about all of this added complexity/cost/work.

Just replace it with a quality unit, and go on as usual. Test the batteries once a year if you're nervous. Worst case if it dies on you, just disconnect it until you buy a replacement.
 

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The science for not paralleling non-identical batteries is based upon charging such a system. Due to AGM engineering and lead-acid chemistry, prompt and accurate charging (along with discharge limits) is essential for maintaining battery bank performance over time. Charging is governed by Ohm's Law, which explains why non-identical batteries in a single bank system will experience unnecessary electro-chemical damage (likely non-identically).

A system which has non-identical batteries needs non-identical charging for each battery, which is not provided in stock Wranglers.
This explanation is not wrong per se, but is in my view incomplete in the real-world context of Wranglers and this thread.

The batteries are not connected in parallel 100% of the time. The moment an ESS event is triggered, the system introduces different depth of discharge between the batteries and begins it's never-ending, permanent differentiation of the internal resistance of each battery.

The benefit of 2 same size batteries starting with (near) identical internal resistance at manufacture is lost. And, any minor starting difference in internal resistance between different capacity 12V AGM batteries will likely be overwhelmed.

In the context of this thread, relocating the aux battery by extending its cable will significantly affect the resistance difference between even 2 same-size batteries and the single charging source (alternator) - which is not a claim the orginal factory wiring is inherently balanced.
 
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Nvdardx28

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What are the physics of dissimilar size batteries causing battery wear?
There isn’t really a fundamental problem with parallel batteries. If there was a good reason then they wouldn’t do it. The only slight disadvantage is that over the lifetime of the battery, the smaller battery will not get the amount of cycles as the larger battery, it will cycle more. This is due to the imbalance of how each battery shares or divides the current either during charging or discharging. When there are two batteries in parallel, current will slosh around between them for a little bit until they balance. This action will shorten the life but not by much. If the batteries were the same size and in parallel, from the same manufacturer, the balancing would be better but there are variations from battery to battery. The balancing is worse when the battery sizes are different but like it said it doesn’t affect the life that dramatically.
 

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This explanation is not wrong per se, but is in my view incomplete in the real-world context of Wranglers and this thread.
Hey Thaw, you asked "What are the physics of dissimilar size batteries causing battery wear?" The question was reasonably related to the thread's topic and discussion flow, and it seemed to be asked in good faith and not as some sort of rhetoric or sarcasm. The answer--the science behind maintaining AGM performance and longevity--is not context specific.

By the way, based upon well established electrical engineering principles, unless aux battery relocation to the rear calls for wrapping cables three times around the seats, any concern regarding a resistance differential from extended cable length is adequately addressed by cable gauge.

Best of luck in your electrical endeavors.
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