Question for Those Smarter than Me

[Wolverine]

Wow! That's a lot of information. This is why I will be having the solar array on the Orion installed by a professional. Too complicated for this simpleton.

Okay, I'll just connect the two identical batteries in parallel and charge them that way.
 
A big thank you to all for your knowledge and help.

[Charles Brennan]

Wolverine, Thinking about it some more, I realized that the BMS (Battery Management System) on many LiFePO4 batteries require a higher voltage differential to initiate the charging sequence. It's entirely possible that a battery hooked to a load output, whose voltage did not meet the charging threshold that the BMS required, would just sit there and do nothing.  It would effectively be deaf, dumb, and blind, to all the energy sitting there at the output terminals, but below the charging threshold.  An Old-Fashioned analog FLA (Flooded Lead-Acid) battery would have no such problem, replenishing from a lower voltage source.
Just another example of how different these newer technologies are and how much you have to keep the entire system circuitry in your head, to keep track of all that is happening and when and how much.
A life-time of FLA experience is of little help, in what is essentially a whole new ball game.

And finally, NOW! I think we've sufficiently beaten this poor horse to death!! 

Hope this clarifies,
Charles Brennan

[pgandw]

Ziradog, You are indeed, correct about inverter conversion inefficiencies.
I had other uses for an inverter anyway, so I just chalked up the conversion losses as a cost of doing business.
I had checked into that when I first got my CPAP machine and at the time, only ResMed had 12 VDC converters and none of theirs matched the connector on my machine.
I also toyed with the idea of making my own 12 VDC to 24 VDC up-converter and wiring it up, but was leery of voiding my warranty.
Thanks to your advice, it might be time for me to look around again at the market and see what's available, especially if you can find one for $30, instead of the $100 - $150 prices I saw back then.  My inverter actually costs LESS than those adapters!! 

Thanks,
Charles Brennan

Charles
Here's a Resmed CPAP adapter to run off a 12V cigarette lighter plug for $30 - https://www.amazon.com/gp/product/B0DMJTJ1H1/ref=ox_sc_act_title_2?smid=A3SU36G3ZQVO8S&psc=1  If the ResMed plug won't fit, find one that will, cut off the ResMed plug and wire the new one on. Just have to keep the polarity straight.

I'm in the same situation, so am looking at installing 12V plugs in both camper and boat.

Fred W
Stuart (ODay Mariner 19)  Sweet P