A hearty hat-tip to RKETR for this thread--I've been running one of the stacked dual battery setups in my Rubicon and disliked it for several reasons:
--The lower battery is impossible to see;
--relocating the electrical box to make room for the upper battery precluded installing an Airaid intake;
--In my view, they are fire hazards with side terminal Optimas--despite using additional shielding, I had one battery almost short out to the tray due weight/compression/vibration tearing insulation almost down to the terminals
--very hard to access terminals if you need to use jumpers
So when I saw this thread, I took the hint but a slightly different route--I can marginally tack fairly thick metal together but wasn't about to try to tack weld to sheet metal in the firewall. I'd have a hole, and likely a fire. So I fabbed a cradle for the batteries, following the general layout here.
First I had to nip off a couple protruding screws--Dremel time.
Next, using 1/8" thick angle iron for the side bars, I tacked 1/8" flat stock to serve as a cross bar. After several dry runs where I riveted a dummy setup together, I bolted the crossbars in place (3 using the original holes; I drilled the after/driver side hole so to give a better, more supportive angle to the crossbar; used the same retaining nut as stock) and with the one angle iron in place, tack welded it.
Then I pulled that out, and built the rest of the cradle on the bench, riveting it first, trying it, then welding it. I could have used just two cross bars, but added a couple and put some heavy, closed cell foam on the cross bars to provide a modicum of support, damping, and tackiness to keep the batteries from shifting.
The top piece was the bugger--this is the first version; I wound up whittling it down quite a bit to get clearance on the wretched connection block that mounts to the firewall. I could have remounted that a bit higher but that was more work than I felt like at this point.
I also discovered, to my chagrin, when all was bolted in place, the driver side battery was just touching the A/C can. So I did some strategic whittling, and gained 1/4 inch. BTW, the none-side terminal battery is a tad smaller than the side terminal; would have been a tad easier to do this if I had two non-side terminal batts instead of just one. Anyway, here's the installed setup, with a messy, temporary job on the cabling. I need to re-run that anyway was the Airaid intake I added at the same time had a little impact, and I'm getting some heavy duty terminals anyway for all the connections.
Lastly, to preempt some of the observations I've seen in this or other threads:
Are dual batteries needed? Ans: Depends. I want them because I hike and hunt a lot in remote places, alone, and a dead battery in bad weather in a deep canyon on a hot day is not a problem I want to solve. Right now my setup is two batteries, isolated, with winch and accessory lights run off one, starter/stock vehicle needs off other. Warn isolator has worked fine. If you're not prone to put yourself at risk as I do, then a heavy duty alternator and gel cell battery will likely do you just fine in my opinion.
Airaid--not the topic here, but the mere mention of CAI seems to provoke debate so here's my two cents: I've seen enough credible research to show it does give decent hp/torque boost, albeit at mid/high ranges. But that helps me, as there are two nasty pulls going north out of Phoenix and one coming back. As I haul water up and firewood back to my little place in paradise, it's nice to have a bit more power. And it makes a difference in town--as if I pulled maybe 200 pounds off the rig. Not startling, but nice. If I lived in a flat place, or didn't drive at high altitude, I wouldn't have messed with it.
So there you have it. This solves all my gripes with the stacked setup, cost a heck of a lot less, and turned out to be mega-fun as I used a self-darkening welding helmet for the first time and it improved my welding by about 300%. Not that it makes it fit for public viewing, but I had fun....