Alot will depend on what you have for an inverter and Ups's.
I have an OLD APC UPS 800RT and it puts out 600watts as I recall. I have it connected to 2 115 amp hr deep cycle batts for 24vdc. Rather it be 12v but it was set up with 4 6v batts at 24v originally. I run a digital clock, transformer for the cordless phone, a light when power goes off, and various other stuff at times for testing. It turns on without 120v power and will run from batteries only. With 120v it keeps the batts charged. I plan to run this off the 5000watt Aims inverter I have.
If the main Batt bank gets low/dead my important stuff will still run off the ups for a long time! I disabled the buzzer (broke it off the board) even though the UPS had a button to disable it. We loose power a great deal in S MO, Howell Oregon power co-op is the worst most incompetent power company I ever saw in my life of 44 years and I have lived all over the USA, mostly rural areas!!!! That said, I disabled the batts the other day because I needed the cable elsewhere, I just looked and the clock is flashing again!! Less than 48 hours and the power been off twice long enough to kill my alarm clock! So far that setup works good when I keep the batts connected to it.
I have a couple 350watt APC ups's but when I connect those to another inverter like the RT800 or the Aims 5000watt the 350watt one clicks and clacks alot like they are switching on off or back and forth from 120v to batts and back. I don't know how they are going to work out when I swap to all batts and inverters. I may need to run those off a small sinewave inverter instead of mod wave or get others instead.
As I recall my larger UPS for my main computer runs fine off the Aims Inverter also.
Maybe a better inverter would also run the smaller Ups's better.
I plan to do something similar to what your doing. Setup the main battery bank away from the house and mount the inverter there then run 120 to the house. In the house all the computers and a few other important items will run off a few UPS systems. I agree with you about lower line loss with the 120vac over 12vdc plus you can get 100amp or 200 amp ac mains line anywhere much easier and cheaper than 100amp 12vcd lines! I don't give a flip about codes, but where they matter welding cable often does not pass from what I've heard, even though it is best.
As for a loss using the UPS to charge the batts at the house, it's worth the little we loose I think for the security of having the backup if the main system goes down or we have to shut it off to work on it. Some things we just don't want to shut off, like the wifes computer just so I can play with the mills or batteries!!!
