You have the same separator that I have (except mine isn't bidirectional - 1314) . It's a good unit.
So what are the deets on those batteries?

Let me finish my tray and then I'll think about replicating my design ;)

They are just run of the mill deep cycle batteries. The specs are on top. Group 24, 130 minutes.

Maybe in the future I will have someone fabric a simple rail with a heavy piece of Angle Iron. Make it all one piece and I'll install a third battery. Not likely that I need it but.. by the way, it doesn't bother me that I can see the batteries. Gives it that hard core hidden industrial look.

That's what I used ... angle iron

It's working out pretty good. Today is the second time I have had to jump start the truck. The first was yesterday I think. I left the keys in it with the accessory on, a phone charging and the radio on... killed the main battery. I don't have a switch installed yet, but I touch a 18 gauge temporary wire to a hot terminal and the "emergency power boost" is activated. Pretty cool. Especially if you knew how much downtime and stress a dead battery cost me three years ago. Everything in your falling apart while you try to save it and here's stupid truck constantly dying. I was too much of a mess to figure out the problem. I was a wreck for a LONG TIME. That battery would just make me want to melt. Especially since I couldn't just throw money at the problem. I never did figure it out. For some reason dash lights would stay on and I was using USB Chargers that were sucking more power than I realised. I tried installing a second battery that I had second hand from a purchase of a bunch of things at once, but they were mismatched. They would just kill eachother. Then I bought an "expensive" FAST CHARGER that was junk, but it saved me from having to spend the night on job more than once.

Seems simple now. It all works, it's all fixed. I have to pull the dash out again to get the radio off the main battery and onto the auxiliaries. If I do that, I will have two voltmeters, one for each system and I probably will not kill the main battery anymore. I would almost rewire the whole truck so I can ALWAYS start it. No accessories on the main starting battery, but really there is nothing on there from the factory. Nothing I would remove as in most ways they are crucial to operating of the vehicle. Maybe the cigarette lighter jacks, but I never use em anyways.

You shouldn't run down the main battery like that. It does permanent damage.

The "boost" should work automatically without a switch.

Obviously I didn't mean to leave the keys in the ignition and in the accessory position. I shouldn't do that because someone could jump in and steal the whole truck. Privately, I have not really cared about the starter battery. It was a forced buy due to my circumstances and a friend paid for it for me. It's a sore spot because I didn't 'choose' it. It was just something that had to be done in a moment of time and that was that. I think I bought the cheapest 'recommended' battery to save his wallet. Realistically however, it's fine. It's likely a good battery, it's sore spot as my mind was set on something else previously.

Boost

The 'boost' should work however you set it up. I do not want it to work automatically. I even questioned using this isolation system because I want to be able to force separation. I might even install a switch on the ground lead. If I do that and the switch is in the off position, I will have my forced separation. A push of a button or a flip of another switch will give me a boost. I was thinking about that yesterday. A double-pole double-throw switch, ON-OFF-MOMENTARY would be ideal Actually, OFF-ON-MOMENTARY would be ideal. That would give the ability to label the positions: OFF-AUTOMATIC-BOOST.

Solar Power

I doubt I will find an acceptable and attractive way to do it, but it would be cool to have solar panels on the top charging the auxiliary battery bank. This would give the allotment of time. If both batteries compartments were dead or run down, time would fix it. I do not know how long these two deep cycles last under x-load, I don't even have a volt meter to watch them independently, but one day as a project down the road if I find panels I can add out of common side, I might do that.

It only connects the circuit when the starter battery is fully charged (thereby charging the Aux), or when it's needed to start the engine. What's wrong with that?


Easiest way would be with light duty roof rack components.

Easy enough. Lets say 100Ah battery, 10A load. 100/10 = 10hrs

Princess auto has some attractive gauges.

It operates according to several parameters determined by whatever circuits are built into it. It's a great little connector. Simple to install. Job finished. It's just that I do not want it connected under certain conditions. It's fine for now. Down the road if it's a problem, I can easily change it out, or at least modify the install. Breaking the small ground connection, inserting a switch or a relay there, is a hard OFF. The other issue I considered was a hard ON. There is no way to force it ON (without subjection to it's internal rule-sets). At 100 Amps I didn't think it would be adequate at first, remember I was thinking up to four batteries, but for a charging/additional boost system it's fine. Everything else will T-Off before that solenoid and connect directly.

You'll be happy to know I am setting my amps up inside. Old Plan #368678. They fit, laying on the raised floor right behind the seats. The rubber mat covers them (heat issues?). I am setting that up today, or at least I was trying to. The idiots wanted $30 for 1ft RCA Connects. !@#$% off. I am not paying that. I wasn't born yesterday. I'd prefer to make my own, but I cannot find SHORT male solderable RCA connectors. Personally, I do not like that connector. It is far too large for what it is. It's not the 1950's any longer. Anyways, I pulled out a spare temporary amp and I am putting in my amps, I just I had one more. One more good one. One day I'll pick one up cheap.

I have been trying to do way too much. I just need simply, get it done and drive the stupid truck. I made a project out of it. All my ideas were great as an after work hobby done over the long haul, but... it's been too long already. This stupid audio system, if it wasn't for that delaying everything, I probably would have set everything else up. I thought I was getting a screaming deal when I bought it for next to nothing, but all I gave myself were more plans and more plans. I've never cared about a radio in a vehicle before. Mind you, I could never watch video's, or browse the internet before either so... tit for tat.

The boost switch is the "hard on"

Not exactly. It has a mind of it's own. There is built in logic. Read the manual.