Looking at some UPS units. Not too clear how long the battery lasts, eg.
This one says it has a sealed lead acid battery and you can get replacement batteries for it
"APC 1000VA UPS Back UPS Pro mini tower backup power supply ..... Hot swappable batteries Ensures clean, uninterrupted power to protected equipment while batteries are being replaced"
"Hot swappable" means what exactly? Are there two in it so it keeps running while you swap out one at a time? Can you recharge the battery after the power comes back on?
I have seen those "power box" things that seem to do what I want that you can recharge, but I don't know about fan noise with them if any.