Adding a 3rd battery to a National Luna Dual Kit

[1leglance]

Ok I did some searching and could not find an answer so I am starting a new thread.
I have the National Luna Dual Battery kit that pairs up 2 small Odyssey batteries under the hood.
Travis of Safari Pacific did a great job on the dual battery tray and starting on the small Odyssey starts the diesel no worries.
However I am finding with the summer heat my National Luna Weekender fridge is really drawing down the aux battery.
So my thought is to add a 3rd sealed battery to the rear of the rig placed inside one of my storage boxes.

I already ran a heavy gauge cable (the one that comes with the kit) to the back for my Extreme Outback Compressor & aux fuse box.

So my question is....
Can I just wire up the new 3rd deep cycle battery + to + and then the neg to frame ground?
Then I will pull off the the + to the aux fuse box & compressor.

Any issues with this setup?

I am looking to add something big to the back as I have the space and I love keeping the fridge running when it is 116 deg here in Phx

 

[Backroad Explorer]

Hi Lance
Are you using your starting & 2 aux. batteries under the hood?
I was looking at the NL site and I can't see any problem running a 3rd battery as long as you run both +/- from the forward batteries to the rear maybe a little longer charging.
NAPA Auto Parts sells Jumper Cable in bulk it is bonded together with molded stripes on the pos. side.
Might be a little easier to run along the frame that way.

 

[1leglance]

This is my starting & #1 aux battery along with the National Luna setup.
My desire is to make use of the battery gauge cable I already ran towards the back for the Extreme Outback Compressor & aux fuse panel and then run the ground to frame rather than run another wire all the way to the back.
So it would be + to + and neg to frame.

Any reason this would not work for the 3rd battery?

 

[dwh]

It'll work. There are issues, but whether they are deal-breakers is up to you.

The main issue is that tying one big battery and one small battery into a single bank will make the small battery work harder and wear out faster. But then, using two identical batteries of different ages will do the same thing.

Using the frame for the ground is a bit dodgy, but it does work so if it doesn't bother you, it doesn't bother me.