Agreed Cuppa,
The VSR arrangement only works efficiently if the second battery is in the engine bay.
The V Drop is the limiting factor. Yes the time frame was without driving/using the alternator at all.
To live off grid and only have to source water is the end game for me one day.
To be self sufficient pending usable solar input is getting better all the time with new technology allowing for amps to flow even in cloudy conditions. I will do a little home work on the red arc arrangement you mentioned in the other post. I envision it to be a pretty solid peice of kit.