A 2 watt CPU seems liker massive overkill, you really don't need that much CPU power. I'm reminded of PDAs from the 90s that could run for almost a month on a s

A 2 watt CPU seems liker massive overkill, you really don't need that much CPU power. I'm reminded of PDAs from the 90s that could run for almost a month on a single set of AA batteries. If you were designing a devices from scratch, it might be worth considering a large (640x300 or larger) transflective lcd display from the late 90s, a keyboard, large amounts of reliable flash storage. It seems overkill to go beyond an ARM M4 for CPU, though a cluster of Cortex A55s might make more sense, so you have an MMU. Give it flexible power input so it can run off whatever power source you can scavenge. From a few triple AAA batteries at the low end to 48v lead acid batteries at the high end. Or a highly variable power source like a rigged together windmill or scavenged solar panels.