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Find a local electrical supply house, they're usually wholesale. It's that or a place like Home Depot or Lowes.

 

Welding cable is nice when flexibility is needed but an added cost if not needed.

http://shop.genuinedealz.com/Welding...LDING%20CABLE/

I have received nice tinned wire from the above dealer quickly with free shipping.

All batteries should be vented if installed in the cabin, but AGM batteries like optima or odyssey are unlikely to outgas unless severely overcharged.

Use as short a run as possible between batteries, and add another fused cable from cable (+) to the battery 1(engine battery) side of the solenoid.


The connectiions are just as important as the cable. Cold solder joints will fail, and it is hard to get such large connectors soldered without melting a lot of insulation.

I have a set of hydraulic crimpers which seem to solidify all the strands within the lugs and make for an excellent connection.

 

Welding wire is some pretty awesome stuff, but it is difficult to make a good solid connection. You shouldnt need to relocate the starting battery unless you really want to. Sounds like more wiring than you need. Run the lead from the second isolator terminal to the positive battery terminal of the stereo batt and you can ground the negative post to the frame. Your not running a 24v system so the second battery can be put whereever it is convenient for you.

 

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I've got 2 deep cycle crowns(group 27) under the floor behind my driver's seat. They weigh 2 lbs each. They are hooked to my engine battery through a manual switch and ~ 12 feet of 2 awg cabling.

I have an older group 27 everstart under my hood. Same size as the Crowns but 12 pounds lighter.


I have seriously upgraded my charging circuit.

My '130 amp' alternator has produced ~110 amps with depleted house batteries when cold at high rpm, but this number quickly falls to ridiculous low numbers as the alternator and wiring heat up. I have a digital ammeter which sees alternator amperage and counts amps into and out of the batteries.

Once the batteries reach 14.5 volts, as little as 9 amps are required to hold them there so even if I got a 200 amp alternator, it would not recharge my batteries faster, unless I was needing 100 amps to run a stereo or winch at the same time.

But even with a smaller pulley on my alternator, Hot Idle speed amperage is truly pathetic, and idleing the engine to recharge the batteries would be wasteful in the extreme.

 

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I am not a fan of isolators mostly due to the large voltage drop, but something electrical surrounded by heat sinks also screams inefficiency to me.




For automatic isolation, I'd much prefer a 200 amp continuous duty solenoid, activated by the blower motor circuit, since that is not active during engine cranking.

http://www.texasindustrialelectric.com/relays.asp

I just use a manual switch and have never had an issue with forgetting to isolate when I need to. I have enough battery and solar power that isolation is not really a factor in my usage anyway.

But man o man does the engine start in a millisecond when all 3 fully charged batteries crank the starter.

 

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Well, in my case, my engine battery seems to have a fully charged rested voltage of 12.8 where as my True Deep Cycle Crown$ are at 12.6.

Since I care about the Crown$ more than the nearly 5 year old engine battery, I don't care if the engine battery feeds the Crown$ when 3 are in parallel and not being charged.

But usually I disconnect the engine battery at sundown, but if I forget, no biggie as I don't have a big enough draws/loads to empty 3 batteries in one night, and my solar is capable of returning 90+ amp hours in a good day of sun this time of year.

I like the switch cause I can dictate where I want the alternator amps to go.

A lot of days I don't bother feeding the house bank, and some days when the house bank is really low, I remove the engine battery from alternator current so it all goes into the house bank. Removing the fully charged engine battery when the house batteries are very depleted also seems to allow the alternator to produce more at RPM, as 14.5 is not so easily reached with the fully charged engine battery removed from the loop.