needed.
the flat metal is marked for cut

 

With only two and 1/2 threads sticking up you are not going to have room for a lock washer or locking nut. Locktite will not have enough surface area to help much. I would watch that close. Any movement of the cables could loosen that nut.
I put on some of those temporary "emergency" clamps just to layout how I wanted my cables to run and get me to the shop where there was a hydraulic crimper. These will carry the full gauge of the required size cable for full amperage. They come tapered to fit tapered posts and in a different size for positive and negative.
After swedging them I slid the shrink wrap over the ends and heated it to help keep moisture from wicking up the cables. With sealed batteries there is very little if any corrosion.

 

When you cut that plate and drill a hole and insert the bolt, won't that give you even less thread? Maybe a longer bolt would be better. Hopefully you could trim the plate enough to get some shrink wrap or brush on insulation on there.
If not maybe boots like I used would insulate the exposed positive terminal.
I have also found that using plated hardware, corrosion can be a problem and I try to use SS in those places. Even though it is a dissimilar metal than the lead or tinned metal terminals, on a car it seems to work. Electrolysis, in some cases can be a problem on boats is why I say that. But that is usually between aluminum and SS and I use anti-seize to help reduce that effect, on boats. Having a nice clean terminal is key to dependable connections, especially offroading.
Lets us know how it comes out.
Mod on!

 

Rather than a diode a switch was my choice at some point. However in my setup I chose to just remove a cable when in a situation I know I could be stranded or heavy winching to save the extra battery. Normal driving I run it all together.
I also planned at some point to install one of these isolators that will charge each battery separately so one does not pull down the other. I use these a lot in multiple battery systems on boats. So good for muddy water and mud being thrown up they are sealed.
I was being brief in my post but since you asked,,, lol, here is the long story,

Revised again! 8/12/11 (added isolator pic)
I used the battery vent hose for the cable run from the winch. I really don't need to spray the batteries with crap thru that thing! I put a reflective coated neoprene pad on the side of the battery closest to the engine and it was long enough to cover the ends. It is still the same distance from that wiring harness the battery tray was. I did not push them over but did release them from the tray and removed the plastic tray. The battery is two inches closer to the engine than it was.
I decided to go "KISS" on this for now. NO switch, or isolator but I can just remove a terminal or swap the main lead.
I want both charging all the time, more amperage for winching and can always disconnect one jumper to save one hot if I'm winching with the engine dead so I have a gauge on what to try next before reconnecting it. That eliminates extra cable and simplifies the setup.
I used the screw terminals for the jumpers between batteries and attached the winch to those. I have now updated those to 2 Gauge 7 1/2 inch instead of the 2/0 which allowed me to bend them in over the batteries. I used welding cable with heavier insulation and fine flexible wire. I used copper lugs that were tinned with closed ends and a special crimper with shrink wrap. I also have an open pos and neg terminal for my rear winch connections.

Exide Marine dual terminal deep cycle.
CCA 750 @0* CA/MCA 950 @32* more like Arkansas weather!
compared to AC Delco
CCA 590 no listing on the battery for CA/MCA

I replaced those OEM main terminals. I decided to just torque one past the point I consider safe to see if it would ever tighten enough that I could not move it. It begain to buckle underneath and actually loosened it. Snip!
I have now Hunnerized the new main lead terminals. Universal ones don't fit the negative tapered post. Those first ones I used in the proto-type are those "emergency" style you find everywhere. You will have an emergency if you depend on that crap. They do not even provide a tapered nut anymore, so it does dig into the lead before it gets tight! I drove the 60 miles to my Brother-in-laws electrical automotive shop. You think I'm pickey!!! He has a great selection of special fittings and several high tech crimpers. We used the hydraulic ones and they are CRIMPED without deforming.
Looks like a candy store!








We had to make some custom dies for the hydraulic crimper to keep from distorting the fittings. We did it in two stages with two dies. The one that came with it are for larger wire and terminals. Like for John Deere's. That of course required us to machine our own dies on a verticle milling machine. Another excuse to play with neat machines. He was busy so I got to use his special tools. I used lead coated copper fittings with closed ends and sealed them with shrink wrap lined with adhesive that when shrunk really seals things up. So I did not pursue the marine grade tinned wire.
This is my protype shot using shop supplies I had, to mock up the cables before going down there.


This is the progress for now.


This is a detailed install and so was written for someone considering doing it. It is not "lite" reading.
Unique to these batteries is the two holes between cylinders that on top is capped off by the thickness of the blue top piece. The difficulty on the H3 using the existing base for the second battery, the position closer to the engine, has for some reason a large hole right where I needed to drill. Then the other hole would line up with a contour edge. I center punched and drilled that one. Then the problem is the bracket is formed down to the fender liner. That leaves a folded seam where these two come together and would not work to drill thru and install washers and nuts.
I went with "J" bolts found at any autoparts store except I made them "L" bolts by straightening the ends to a level position. Use at least 5/16 that was as big as I could find. Here comes the most "tecknackle" part. Caution this involves duct tape! I stuck them down in the two holes in the base and taped them so they would stay oriented with the L under the base plate. I just used spin on nuts, lock washers and locktite on the top to keep from turning them. I left the threaded part a little long. Im considering running a brace across the top of the batteries just for good measure. Hunnerized!
The battery closest to the fender I used a long bit clear down thru the fender liner. The liner is not against the fender so would not allow for tightening. I used a die grinder to make a hole for a socket to fit up in there to hold the nut. I use stainless for everything since I had most of it and it will allow for easy removal. I used 3/8 all-thread and put nylocs on the bottom end to hold that in place and was able to use them on the top while holding the bottom. It's a stretch to reach!
The base plate I had to bend down a tab with a hole in it for a wireloom connection to get it out of the way. I then added some neoprene on the slight edge since it is too short and strong to bend.
The SS ubolt in the middle was my first attempt to install a battery hold down strap, fail! Not enough room.




stay tuned a work in progress..................
Found a possible switch if anyone goes that way. It's inclosed so will be protected. I found another place that indicates those panels like you see in the top can be removed on any side to allow the wires to go in.

Battery Switch with **** from Wholesale Marine

Here is another for a little more money but not as boxy.
BEP 701 Master Battery Switch at West Marine 710 1641&Ne=0&Ntt=Batteries &Ntx=mode matchallpartial&page=CategoryDisplayLevel1&isLToke nURL=true&storeNum=5002&subdeptNum=9&classNum=297
This is the isolator to separate the charge from your alternator to the batteries. If using a switch this will allow charging the second battery when off to the main output. When combined with the switch it will prevent a weaker battery from pulling down a better charged battery while charging both as required.

 

What Hunner did is the MINIMUM I would even consider doing.

I personally have not, and will not install anything other than Higher end stereo terminals.

 

Not being familiar with high end stereo terminals, only the ones that a set screw held the wires, I wanted a strong physical connection as well as full contact of the gauged wire. So I went with the farmer, tractor, grain truck, marine fix I grew up with. I have seen guys carry a battery by holding a wire connected with these.
Nothing runs like a Deere!

 

and you know I'm not cutting down your work.... your install is very clean, Hunner.

 

quote drtom "hunner , i consider your "fix"the "nasa"!!system,,it aint gonna fail!!
I don't know about that but it won't do ME any good to call "Houston, we hava problem" in the middle of nowhere! lol
quote Muddy "and you know I'm not cutting down your work.... your install is very clean, Hunner."
Glad to hear that, but I did think you were pulling my chain! lol
Hell when drtom and I first got cars, they did not have stereos!!
AC was an option!

drtom, they turned out nice now that I see how you did it. You gots a place to connect that new winch you always wanted! Just remember to keep your nuts tight!!

Remember my install of the batteries is in an Alpha. I never got "aroundtoit" on my 06 I-5. Yes I had to cram some wiring out of the way and cut some wire ties and add some. Brake lines were close.
I used that insulation blanket around my batteries. Maybe some on the bottom would have been a good idea.

 

Here is where I said what Hunner did is the minimum I would do.... again... his work is awesome... but I need to have foolproof failsafe.

I have a National Luna Intelligent solenoid I bought from Sierra Expeditions. If you have never checked that site out... woowee... what a nice site. Sierra Expeditions

ANYWHO.... my batteries can be manually linked to jumpstart, winch, etc.... but they are auto isolated when the main battery falls below a certain voltage.

If you have your truck on a charger, like Hunner, who uses a solar charger... the solenoid would close and allow both to be charged, once the main battery is taken care of.

I love it, and I give it 5 stars. I expecially like the monitor.

National Luna DIY - Split Charge System

 

This works now fine for me...

Gold plated connectors and a Optima battery.
Fits great in the slightly modified casing.