What is the most powerful computer that can feasibly run off of two (or four, at most eight) AA batteries?

I've considered getting a Game Boy Advance or Wonderswan so I can play those games in their intended environment: but I'd prefer something that's more general purpose, complete with a keyboard.

As for battery life, I'd expect the thing to last at least 4 hours.

#askfedi
#retrocomputing
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