The following is not a new proposal around here...intall a single Group 31 100Ah under the hood...use a JSS tray for 3.8s or modify the factory box to accept a single battery (3.6L motors) Then if you really need it, drop a 2nd battery in the rear for when you need the add'l juice.
A dual battery sounds cool...but is it really? I'm not sure most people realize that a dual battery setup results in a ~20% of the usable Ah...and no more than the stock Jeep JK setup.
Math:
Jeep dual setups : Two Group 34 PC1500 Odessy Batts @ 68Ah. = 2 * 68Ah = 136Ah under the hood.
One reserved for starting, one for Aux - sounds great.
Apply 50% guidance to maximize battery life vs cycle : Result 68Ah x 50% = 34Ah usable for the Aux Battery.
34Ah /168Ah = ~20 % useable capacity....doesn't sound great anymore - especially at cost/complexity these dual batt kit guys are charging.
IF the batteries are indeed 50-55Ah, it makes it all the more reason to rethink a dual battery setup.
Rethink:
Install single Group 31 100-110Ah Battery
Apply 50% guidance to maximize battery life vs cycle : Result 100 or 110 Ah x 50% = 50-55Ah Usable.
34/55 = ~40% more usable capacity with a single Group 31.
If you do long, excessive pulls in a work application, then run a second group 31 battery in a battery box in the rear of your jeep. Run 1/0 or #1 cables + Andersons from the underhood battery to the rear battery when working. After a hards days work, connect BOTH to a decent shore charger - unless you're driving >4-6hrs each night, your jeep will not properly charge those batteries for another day's work and you'll be well into defecit cyclng territory.
I ran the Sears Platinum batteries for several years until they were offered no more. After 4 years, there as a decent loss of capacity. At 6yrs, I was well past 50% lost and it was very noticeable running the various loads.
Now I use Sam's Club Duracell Group 31 100Ah Deep Cycle batteries for my main battery. I'm really liking these batteries for the money....I can buy 2 of these batteries for a single Northstar....no way will I run a battery long enough to justify the 2x multiplier - I'd rather replace my Group 31 Sam Duracell Deep Cycle every 3 years and still be ahead of the Northtar costs at a 6yr replacement interval.
I have NEVER killed my single Group 31 battery enough need my Aux jumper to start my Jeep - winching or otherwise.
I've run a Dometic CFX63DZ fridge, communications (ham and other) gear, and other electrical equipment for 2-3 days without worrying about the starting battery in relatively hot temps. I typically will run 1-2 200mm fans mounted on custom window vents to keep the jeep ventilated at night or while napping. My dog really kicks out some heat.
Side note:
@jacobconroy - doing some math on your numbers suggest you've pulled ~66Ah in a single night. That is a ton of juice....you may want to rethink your loads. That fan for example: invest in some computer fans of the appropraite size & location - quieter, will move the same amount of air and much more efficient. A National Luna fridge pulls 38.4Ah in a 24Hr period? Wow...that is A LOT. Get a cover and install some fans to let that thing breathe. The JK charging system will produce 14.5V on a regular basis...this is more than sufficient to charge most AGM batteries. Some batteries mfrs, like Full River need more voltage - and would require an additional charger. (I still like a TUNEABLE B2DC however, as it allows two things: (1) create a regulated DC bus for senstive electical gear (2) use whatever battery I want. Anything that cannot be adjusted should be skipped...this includes NOCO, CTEK, etc).
Our Jeeps are easy to kick over...so a decent Group 31 depleted to 30-50% has NO problem starting a Jeep even in the cold. (Ask me how I now).
The Jeep Alternator will produce ~160A at ~2500-3k Engine RPM. The Jeep will consume ~25A wiithout the electric fan running and all other accessories off. Add the fan and that load will increase 40A or so depending on speeds. That leaves about 100A - that is enough to run most winches (except at initial stuck).
Side Note: I have since added a 2nd 100aH battery in the rear of the jeep as my electrical loads have increased (I have a work / play jeep). I run a B2DC + MPPT charger to control the charge. Jeep All of my comms gear is connected to the starting battery, incl GPS and phone charger. Fridges, equipment chargers, lights, fan, computers, are connected to the Aux Battery....I'm contemplating leaving all my solar gear at home unless I basecamp for more than 3-4 days without starting the Jeep.
Like one of the posters above, I know also have a van...I will be using a very large lithium setup and 2nd alternator....but I have never felt the need to double the planned battery energy capacity.
Pick your fridge carefully and install add'l cooling fans to prevent the compressor from being smothered. Get some inexpensive reflectix window shields for the rear of the jeep from Amazon or ebay for cheap. Cover your cooler with a WHITE towel or cover.
edited...didnt realize I called his fridge a POS until I poted it.
