12v Power Transfer Switch/Relay

Hi there - Looking for some input on my 12v power/charging setup. My Daily Driver is not a Sprinter, but after searching for some time, I hope someone here might be knowledgeable on this subject. Hopefully this will point others in the right direction as well.
2002 Silverado Truck with dual CS144 series 130 amp alternators, one battery bank (2-50Ah YellowTops), and isolated accessory/start battery. Batteries and alternators are currently isolated via Charles StartNow relay (which really only isolates batteries in dis-charge state).
Ultimate goal is to be able to run stereo and accessories down to low voltages and have no problems starting vehicle. I am trying to setup two completely separate circuits (battery bank being charged with future smart externally regulated alternator, and start battery/alternator powering all systems, including 150a max. stereo).
Upon turning off vehicle, the power source would be switched from starting battery/alternator to aux. battery bank. I love the idea of having a 100% fully charged battery bank being charged in float at my disposal every time I turn of my truck.
All the transfer switches/relays I have come across are of the 120v/12v type (marine-shore application). Is there such a thing as a 12v/12v transfer switch? I've thought about higher amperage relays, but this setup would involve dual inputs with common switchable output.
I like the idea of my truck running normally, and want to isolate the voltages that are sometimes associated with charging a depleted battery bank via external regulator from the normal operation of my truck.
Brands I've been researching are Xantrex, Sterling, Balmar, Charles. Can anyone suggest others?
Any and all input-comments welcome. -Nathan

Hi Nathan,
Have a look at this site:

http://bepmarine.com/home-mainmenu-8/productcategory-44/voltage-sensitive-battery-relays

These are available in USA at various outlets. Check out ..... http://bepmarine.com/index.php?option=com_webpage&id=85#northamerica
I have a voltage sensitive relay in my setup.

Cheers

Ross

I used the SurePower 1315 bi-directional smart relay to separate my starting battery from the house bank. You might go cheaper with the unidirectional 1314 if you're not plugging into shore power.

Sounds like you should move the stereo and/or other accessories to the second battery. That would help prevent running down the starting battery.

I did wire the optional temporary override into my SurePower and that allows a start from my house bank if I do something stupid (like leaving a cab light on for a few days...)

Dan

Thanks for the replies guys. Done some more thinking and think I need to clarify what I want to do.
I originally bought the Charles StartNow as an alternative the BEP VSR (cheaper), and at the time, simply wanted to isolate my starting battery. Starting system has worked well for nearly two years, except for boosting a few really dead vehicles (blew one and a half 200a fuses). StartNow didn't hold up, acting funny now (not closing circuit). Regardless, isolator will not be needed with new setup.
What I am planning now is to have two completely separate power source circuits and having the setup automatically switch between the two, depending on whether or not the vehicle is running (charging). First power source circuit would comprise of AGM battery bank with externally (or not, will have to see if needed) regulated charging alternator. Second power source circuit would be made up of second alternator and starting battery (direct wired to starter).
My issue is the switch to the factory distribution panel and stereo that would allow automatic switching. Upon further investigation (haven't found such a product), I am forced back to the basics, which may simpler and will definitely be cheaper. Has anyone used high current 'normally closed' relays?
What if I put a normally closed (circuit broken) relay between my aux. batt. bank/dedicated charging alt. and distribution panel, and a normally open relay between starting batt/2nd alt.to distribution panel? Two completely separate circuits, power source switching between the two. Primary alternator would run vehicle, all accessories, and charge starting battery (ie-identical to factory setup). Charging alternator would ramp up, bulk charge, absorption charge and then float aux. batt. bank until vehicle is turned off and called upon.
I am thinking of using ignition (turn key 'on') as trigger for both relays. Any obvious flaws or conflicts in this proposal? Can u buy something that does this automatically? If it works, it should be rather inexpensive to put together I would think?
Again, all comments, input appreciated - Nathan

How about making it simple. One battery set for the truck as it stands. The second set has it's own charger. The only use is to be a backup starting system. So a simple toggle would make Battery Main or Battery AUX the operating set.
Or simply jumpered together to do the starting.
You could have connections under the hood for the second battery to use it for Jumping other cars.
Like an airplane has for magnetos. A, B or both.

Update:
Here is a drawing I did. You wouldn't need to make the switch automatic. Simply swap when you feel you need to. Since each is on it's own generator, no additional wires are needed except probably at the alternator to also keep them isolated.

Yes, a manual high current switch would be the simplest solution, I agree. I do like automation (start and go). I may add a paralleling switch in case something goes wrong with starting battery. I won't be boosting too many more vehicles, considering the time and $$ in my system.