As long as you're not opening the fridge / freezer during the outage (and you have sufficient thermal mass of food in it) you don't need to worry about "boosting" it during a power outage of only 4 hours. I don't recall the rule of thumb off the top of my head, but for at least 6 hours I'd expect the contents of normal fridge / freezer to be just fine (as long as there's thermal mass there).

The issue there is the plug would be on the battery which you're unlikely to have mounted in a convenient location for things like your main fridge, router, and computer. For me all 3 of those are pretty far away from the most likely places I'd put a battery bank. I have a mobile one I keep charged up for emergencies and long power outages and have a small portable solar panel for it for multiday outages.

I dunno. TBH I'd rather just let the food go bad than bother with the expense and hassle of having a battery and keeping it charged. I guess other locations may have less reliable grids than I do, but I've only experienced one power outage that lasted so long[1] that our food went off in my entire 40 years living in the Twin Cities area.

[1] About 96 hours, major storm took down a ton of trees through the whole metro area that took days to clear.

Must be nice. I live in Virginia, outside Richmond. For the past 8 years, the power company has failed to provide me with even 3 nines of power availability (that means at least 9 hours of outage every year for the past 8 years. Just had a 17 hour outage as of last night, lost everything in my fridge. Again.)