Dual battery, single battery relocation solutions

I recently got a group 27 AGM battery for my 3rd gen. The thing is larger than factory for sure. Long story short the alternator/starter cables are being over stretched and I had to connect the fuse box power cable to a bus bar I had installed previously for other accessories as it simply won’t reach the + terminal.

To add a level of complexity I’m in the process of adding a rear winch.

Okay, back to the subject at hand. Thanks to this larger battery room is tight in the engine bay. It looks like to really do the job correctly with an element of neatness I need to add a bus bar and power all the factory cables through this bus bar. This is fine and dandy because I have a 4/0 I can run to the back for the rear winch. But again room is tight.

solution 2 would be to relocate the battery to the back of the truck. Potentially where the spare tire is since my spare doesn’t fit in there either way so it’s empty space. Where the factory battery is can be used to install a bussbar and neatly get everything power.

3rd option. Go dual battery. Go back to a 34M battery up front where I know everything fits easily. Use the 27M battery I currently have as an aux battery installed where the spare tire is. I can then run the rear winch off of it and the front winch can run off the primary battery like it currently is being used. Secondly the aux battery can be used to run lights and stuff at the camp without worries of power issues or the truck starting. The second benefit to this that I see is that I wouldn’t have to fuck around with the 4/0 cable. Anything high amp draw will be on short lengths of wire and therefor can use lighter cables, e.g. what comes supplied in the box. And the alternator charging cable would only need to be a 4 gauge.

what are y’all’s thoughts and how would you go about this?

I do want to mention that right before I put in this 27M battery I had a 34M. I primarily did this because the AGm batteries weigh more than factory one and the 34M weighed 50Lb where as a 24M weighs 57Lb. My concern here being that I don’t want the support bracket to crack like many have. Granted yes the 27F weighs more either way. But I’ve been wanting more battery for a while so I said fuck it, I’ll cross that road when I do. But if I were to go with a dual battery then the primary can be under sized

 

Now you have me curious -

Youre wanting to run two winches? Why?

If it were me, I would sit down and rethink my setup. I'd bring the truck battery back to stock size group 24. Then, if anything, I would run a light cable to a rear outlet and build a portable power station for the rear, and have it able to charge off of either solar or the rear outlet. The less dedicated it is, the more versatile it is, the more options you have at setting camp, or off-roading, or running weekend chores. I really like the camp battery being 100% isolated from my lets-get-the-hell-out-of-dodge battery.

Why? One, it saves weight and money because I don't need expensive controllers/isolators to manage a pair of batteries that are of dissimilar size, age, and/or chemistry. (Dissimilar batteries directly wired to each other is bad. One will constantly try to charge the other, thereby shortening the life of both.) And, as you said, there isn't a need to run a rats nest of transatlantic grade copper. Two, as I said before, it opens up versatility. Maybe the camp power can stay in camp while out exploring for the day. Or... what if your hitch-mount winch could magically sit on anyone's hitch??? Imagine being able to recover yourself from any vehicle in your party. Portable station could make that happen.


But I'm weird like that, I never saw the advantage of a fixed dual-battery setup. A modular solution would open up more options.

 

Well I have most of the equipment like an extra winch and whatnot which puts me at an advantage. But I’m mostly pursuing this for the fun of it and I think it will be a unique build.

but truck already has solar and a controller. It’s just that I know dollar for dollar I can build a better setup than a power station.

 

and how much over GVW is this truck?

 

I 100% agree with you about keeping weight down up front. I run a 27F as the starter plus a 35 aux on the passenger side of my second gen. If I had to do it all over again, I would use a smaller starter battery for weight savings without a doubt. And with todays battery and battery charging tech advancements I would consider putting the house battery behind the rear seat with a RedArc charger. If I even opted for a house battery, but thats a different discussion..

To your point of stock wires not reaching, I solved that with good quality copper welding wire, compression lugs paired with a hydraulic crimper, and good adhesive lined heat shrink to cover it all up. Allowed me to cleanly splice in the length I needed.

Also consider using MIL spec terminals to your advantage instead of busbars. A bunch of strategically placed ring terminals on the bolts.

Lastly about the rear winch, youll want heavy gauge wire running from the main battery back there regardless of where (or if) the second battery is. If you go through all the work of adding a rear winch, Im guessing youll want to be able to use it. Why limit yourself to relaying on the charge of that aux battery alone for winching? You'll want to be able to access the full power of the system with both batteries and alternator all tied together when winching.