[kaptain]

While I was about to install the newly arrived Xantrex Echo Charge onto my 701, I further checked the wirings. I discovered a new issue: the battery isolator is apparently defective and needs replacement. The defect is that a middle (input) stud is broken or missing, and four (4) thick red wires are connected to one single stud.

This connection seems to purposely bypass the battery isolator to establish connectivity allowing electrical current to flow, but in any direction now, instead of limiting one-way-only flow from the alternator to the two battery groups.

See the attached photos showing the wiring issue. Now I believe the erroneous wiring here (might be as well as the erroneous wiring with Xantrex charge) are intentional rather than a mistake.  And I wonder if this was done by any repair shops or the previous owner. 

   
   

And I created a schematic that hopefully better illustrates the issue: three battery isolator terminals: A (output), B (input), C (output). Now connects A,B,C together - that's the issue.

   

So I started looking to buy a new part to replace the Sure Power 3002 on my 701. This is a battery isolator rated at 300 Amp. "Sure Power 3002" seems a discontinued/obsolete product for some time already, and it is hard to find. A few listings I could find show price over $500, even with used ones.  I found a Sure Power 3003 (which supports three battery groups) that also costs cover $500. 

So I started thinking about my options. Do I really have to buy the same model or the same type of battery isolator?  My understanding is that the Sure Power 3002 basically consists 2 large capacity diodes with a big heatsink. I could buy 2 or 3 large capacity rectifier diodes (prices around $10-$20/each) and build an isolator for under $100, but using rectifier diodes for current directional flow has one major drawback: a 0.65-0.75 voltage drop or power loss.   

My second option seems to go with mechanical relays. Many such relays are sold on Amazon, listed as Smart Relay Isolators, which switch on when the alternator has an output (engine running). When the alternator has no output (engine off), the circuity is automatically cut off, thereby disconnecting and separating batteries. The advantage of such a mechanical-based isolator is that there is no voltage drop like diode-based ones. But these types of relays rely on mechanical contacts to open/close; over time, these contacts go bad, especially switching on/off at an electrical current. 
Here are several mechanical relays seem attractive:

https://www.amazon.com/dp/B084VVGT4T/
https://www.amazon.com/dp/B09Q27WCHM/
https://www.amazon.com/dp/B08SW4XVNR/
https://www.amazon.com/dp/B004WDPZEW/


My 3rd option seems to use a "Schottky Diodes" based isolator, which works the same principle as the SurePower 3002, but it improves the voltage drop by half or ~0.3v (low current) to ~0.45V at high current.

So I kept thinking and searching. I see there is another type of isolator that employs MOS-FET. This type of transistor works great as a solid-state open/close switch over high currency, the advantage is it can reach near-zero voltage drop. Examples of such are made by Analytic Systems, Model: IBI1-40-340 cost about $200, this is attractive.

After considering several alternatives for replacement, I decided to go with "Victron Energy Argo FET Battery Isolator, 200A", which supports 3 batteries, although I only need support for 2.
https://www.amazon.com/gp/product/B00UAN0HBE/

FET isolators allow simultaneous charging of two or more batteries from one source without the voltage loss associated with common diode isolators. I see Victron makes both (Schottky) diode-based and FET-based.

   

Now, here are my questions and a few items I need help on:

1) What is the isolator on your coach, maker, and model? I'd like to see how Newell fast changes and moves from older/traditional isolators to new ones over the years.

2) What would be your choice if you were me?

3) What type of alternator is on your coach? I have a Delco Remy 50DN, Part# 1117860. My alternator is good, but I'd like to read its wiring information.
    I found some documents online about this type of 50DN alternator, but none of such documents contained wiring information.
    https://www.delcoremy.com/support/servic...ion-sheets

4) I measured my house battery negative terminal against chassis metal. It reads about 1 volt. I thought the chassis metal should be ground therefore 0 voltage from the battery was negative against the chassis metal. What's the reading with your coach, with Alternator/Charger cut off both on and off?