@vriska @7666 UPS? those are mostly for blips, and even then only for very sensitive equipment. i mean yeah you can get "eco" UPS that are for like.. keeping the router or alarm clocks alive during a reset.

if its more than about 5 minutes you'll need an ATS (automatic transfer switch) in to some batteries (the gel sealed stuff is cheaper, lifepos are expensive as shit.) what the transfer switches do is run grid power until the grid dies and then they flip over to the secondary systems kind of like a UPS but unlike a UPS it does not run all of the current through the cell all of the time.

you do need an inverter to turn the 12V DC back in to 120V AC. its possible that the electronics still die long enough to trigger a reset in less resiliant ones--these aren't UPS'.

its electrical work so you have to figure out what devices you consider critical systems and then look up their watt/amp ratings. deep cycle cells are sold by their amp-hours, so if your fridge (usually 6-15A) is 6A then a 250Ah cell should last 41 hours (ignoring losses.) i saw the gel sealed ones being about 400$ at this rating. those are good for about 500 full cycles of dead&recharged, but they are also rated on "depth of discharge" so if you don't use them all the way down theres a kind of nonlinear life extension to it.

you can skip the ATS if you want to manually deal with moving the plugs and inverters though.

some nerd i was talking to mentioned taking some of his electronics aparts to convert them all in to DC to bypass this (that nerd was living on solar and doing this to get out of the conversion loss rates all the AC adapters create) its true that DC->AC->DC is retarded, but trying to convert things to run on DC directly isn't necessarily trivial.