The trouble with most solutions is unless you are rigourous about maintenance, they will do a Fawlty Towers fire extinguisher job on you every time you need them, so don't forget to allow for that aspect. A battery based UPS is fine in the right scenario, as is a backup supply. You don't appear to need sustained power, just a backup, so I think I'd probably favour a generator as well TBH. At my last place we had a range of solutions for various systems. Most critical had dual battery UPS fed from A supply that had flywheel UPS to hold up supply while the generators fired up and stabilised (two redundant systems of same), less critical had battery UPS on a different single generator backed supply. All systems got checked on a regualr and routine basis, fuel reserves were montired to ensure they didn't degrade, replaced as required. It can get expensive.