Adding a 2nd battery

We like our old three-way fridge for the ability to cool with fire. Propane is available everywhere in our area and more reliable than sun back in the woods. Regardless, it is time to swap out our two 12v flooded. The last time, when I replaced the once Camping World installed at the sale, the salesman tried to upgrade us to 6v, only to find the their additional height was too much for where the tray was mounted back under the front curve and would leave them tipped. We still have the space constraint and none of the AIs will answer my question “Will it fit?”

If I were spending money on batteries, I would look at every possible option to go with LiFePO4. As Rpod-Couple says, FLA and lithium batteries are so close in price now it doesn't make sense to put up with the limitations and weight of a lead acid battery. The easiest solution is to pop a LiFePO4 battery in the battery box and get a nice, portable solar panel with a built in controller and alligator clip it to the battery when camping. These batteries do get a bit finicky in the cold, but some come with internal heaters to keep the battery warm and they are so light, they are easy to remove during storage.