Just got what you recommended, a 10G inline fuse holder with 40a fuse. Going to get it going today. I don't need ESS to work, I just wanna see if my battery finally gets charged up enough so I can point to my AUX as faulty, even though Orielly's said it was fine. When ESS finally engages for me the voltage starts at 12.8 and drops 0.1v every other second. Im usually down to 11.8v by the time the light turns green. If not, oh well. It will still be good to have in case of emergency and it was only $9.I'd say lower the gauge a bit (i.e. use thicker cable) at 40amps or down the amps to 30 for 10 gauge wire, or buy one of these:
Also--if you want to run one battery I'd recommend that you don't allow ESS to engage. The reason I say this is because ESS may remain on too long thinking the ESS battery (really now your main and only battery with the fused wiring) is chock full of current and that your main battery, which provides the majority of the current for post ESS event engine cranking, is sitting quietly behind the scenes ready to jump in and energize the engine crank, when in fact it is this main and only battery that is getting depleted during ESS events that may drop too low for a successful post ESS engine crank.
Then again it may not. But the 3.6L was designed and calibrated based upon two batteries. Sure, other vehicles run ESS with one battery but the thresholds for when an ESS event terminates because the voltage has dropped too low may be more aggressive in the 3.6JL than in other one battery ESS systems. The Wrangler may push limits with the two battery design that other one battery ESS vehicles don't.