I don't know if I may be of help. I picked up a lot of UPS's, 6 of varying sizes, from 15 pounds to over 100 pounds. I'm not sure if any of these could possibly help your situation. These power 120v AC, but possibly you could get creative. I'm not quite sure what you need to do, and don't know if these could even be used correctly.
It may be that you would get more power out of a marine battery. They make all different sizes. My Brother uses them on a big RV-type trailer. His system was way cheaper than getting a RV battery. I think some marine batteries run 24v, or maybe you could hook two up in series? If this sounds like a possibility, I'll ask my brother where he got his. He worked with a guy that saved him a bunch of money, and he ended up with way more power than a standard RV battery. Obviously not as clean of a solution to what may be available commercially, but you may save a bunch, both on initial install, and maintenance down the line.
