batteries abruptly stopped holding voltage under load...

I've seen you on both forums, and yes they can be hard on people there but I believe other than one poster all intentions were good. You need to be very specific about your equipment and situation, something you couldn't be as you don't really know solar design and electronics . Diagnosing problems via cyberspace isn't always easy. Anyway I have been doing this for a few years and don't feel qualified to give you a solution, it takes decades of learning, doing and understanding off grid solar to be able to be an expert in this field. whoever designed your system isn't one of those people. This became obvious when they set up your rather large system with a rather small 24 volt inverter and small battery bank.

 One comment I will make is this. This is the first time you mentioned what model charge controller model you have. Granted, it being a 100 amp controller and may be rated for 6,600 watts that rating is for a 48 volt system. at 24 volts it is rated for 1/2 of that.  If you want a dependable smoothly operating system down the road which will give you much longer battery life you really need to go with 48 volt. About the only equipment  you need to replace is your inverter, some minor rewiring and size your battery bank properly. I strongly recommend you find another QUALIFIED installer to do this.

Jabroni,
1) What is the Magnum PAE low battery cut out setting (LBCO) on this 24V system?
2) If you have the Magnum AGS set on SOC, you should have a Magnum BMK installed to calculate this SOC... What is the efficiency setting of this BMK? Typically, it should be in the 95% range for AGM batteries. You shouldn't use SOC for the AGS (gen) as you're drawing too much loads for such a small battery bank (Peukert effect), it would be better to start the gen on low voltage only until Float (AGS) in winter, all other settings being Off. I'm not sure that your Honda will have enough gas capacity to allow a complete charge cycle while supplying 3kw load.
Anyway, I agree with all that was said previously on both forums, wrong system voltage (48V), bad system design (go propane), undersized battery bank, etc... Trying to supply this kind of loads in winter was a very bad idea and an AGS to back up the system is not always your best friend.
Good luck...
A+
Erik

I don't like the system design either. As I have said a 48 volt makes more sense and a designer who pushed this with just the size of your array, I would not recommend to anyone. I have a 24 volt system ONLY because I had a smaller system and had purchased the forklift battery. So when I was forced to move to a different place I already had the battery, recently purchased that might last 15 years... If not I would have gone with a 48 volt system.

I have already made suggestions for trying to make your system work. I will add these comments as if I was designing your system from scratch.

Solar does have challenges for heating and cooling, I would not plan on space heating with solar, unless perhaps you are in a particularly sunny area (Where are you located?), and then, as always, it would be conservation first, a very tight, very well insulated space.

I certainly would think cooking is fine with your system (although I would not use the oven, and an oven might draw more than your inverter can deliver) and even water heating, perhaps running your generator at times of repeated cloudy days. I cook and heat water with solar on a slightly smaller system, though I will use a sun shower with water heated on the wood stove at times.  I would not try to heat with solar, they don't work very well together, it's coldest when it's dark and storage is always the weakest part of solar systems.

I suspect you should be able to run an air conditioner on your system in the longer sunny days of summer. You might turn up your temperature setting during the night to 'load shift' and cooling more during the day while you have the extra energy. Trying to keep the load off of stored energy is something to be desired.

I, also would recommend a gas heater, they are very efficient use of energy, Mr. Heater Buddy  (and I had one that I used in my cabin) are Okay, but I found even with proper ventilation, (window cracked 1/2 inch, the recommend 9 square inches of ventilation for air exchange) I got headachy in my small cabin. I would and do heat with wood, and would recommend a direct vent propane heater if you did not want to do wood. They can be vented outside with out going through the roof or even above the roof line. While Me Heaters are not recommended for household use, (from their manual), using one with proper ventilation as a temporary fix until you installed one of the other options would be my plan. Since you would have to burn gas of some type to run a generator, the efficiency is much greater to use it directly to heat.

Link to the cheapest direct vent heater, there are other nicer looking ones;
http://www.northerntool.com/shop/tools/product_200631824_200631824?cm_mmc=Google-pla&utm_source=Google_PLA&utm_medium=Heaters, Stoves + Fireplaces > Natural Gas Heaters&utm_campaign=HouseWarmer&utm_content=44633&gclid=CjwKEAiA79zDBRCgyf2FgeiY-CESJABzr0BMNvuHnFxbX7Gq1cZhLxb2AfG5_1R4DMV_PPoIpXGN-BoCaLzw_wcB

I'll hop in here and first say, Yes, "SunGod" is NOT helping anyone, he's just trying to prove how much he knows and has sent many people anywhere else for help. 10 years ago, I spent a couple hours a day replying and trying to educate him on a now defunk solar forum. I do wish you had gotten a chance to inform him that there are 100 ah charge controllers (and have been 120ah and possible higher). I told him about Net metering when he refused to believe, I was in my air conditioned cabin, when he told me it couldn't be done. I always posted links and he would always not follow them and continue on. He once posted that solar systems were only 90% reliable.... I could go on, and have in the past, He's more a plague than a benefit to Solar forums. I moved this rant to the end since it was so long.

Jabroni,
Did you check if the other settings (SOC, Loads) are really set to Off (I mean other than Voltage)?  I think that 23V may be a bit high for LBCO in your situation, something like 22V for the LBCO and 23V with a 60sd delay for the AGS would be more realistic.
Did you try to charge the bank "manually" without AGS but with longer absorb time (4hr)?
I would also check that the absorb is on Time only (no end current/amps).
A+
Erik

It would be better to have 1 volt difference between LBCO and AGS start. By setting the AGS above 23V under load, you are in the 60% SOC range assuming that your batteries are still in good shape.
From memory on PAE, default LBCO is set at 20V from factory with 1mn delay and can be adjusted from 18V to 24.4V with a ME-RC or ARC (these settings are under load).
BMK can be a bit foolish with such load and SOC (from BMK) can drift quickly, I would not trust it as a parameter to start/stop a gen in your case. Yes, set both to Off and use Low Voltage only (23V max) to start and Float to stop this gen until you have enough sun to charge/absorb these batteries for long enough (assuming that your absorb voltage is right and time set to 4hr).
Did you check the battery efficiency in the BMK setup menu? What this number is?
If that were mine, I would add a second battery monitor (Trimetric) to the system.
Just guessing,
A+
Erik