I usually have at least one of my two power banks fully charged. That extends the 3 - 4 hours (depending on the game) to 9 - 12 hours. My Vita Slim or 3DS XL run even ~30 hours with the power bank, my OLED Vita 20 - 25 hours.
Still isn't much on a full 3 days. But you ended up giving much better solutions.
So yep If I was looking to play through power outage I would rather pick up the Vita I paid 50 bucks than do all the sacrifices on the HW that I use daily just in case I get a power outage of 3 days that never happened in 30 years of my life. The closest I got was 1 month without power at my house because of problems on the provider, but I was more worried at lack of light to read, battery for cellphone and cold bath than if I would be playing on console or HH =p
duduspace11 "Well, since we are estimating costs, Pokemon Red/Blue did cost Nintendo about $50m to make back in 1996"
Mr Puggsly: "Hehe, I said good profit. You said big profit. Frankly, not losing money is what I meant by good. Don't get hung up on semantics"
Azzanation: "PS5 wouldn't sold out at launch without scalpers."