[cstross]

I used a Psion 5 back in the day, and read ebooks on it which gave the battery life a torture test. A pair of Duracell AA cells would last 20 hours without the backlight, and about 7 hours with it.

A Gemini or Cosmo with the wireless hardware turned off and the backlight at about 30% will handily exceed the 7 hours, but not reach 20 hours. Except you can top them up with any USB-C booster battery.

AAs and AAAs are an environmentally wasteful solution: they were great back in the day when laptops sometimes had a mere 60 minute battery life and required a kilogram-sized brick to charge from the mains, but those days are long past.

[criddell]

Your Psion 5 battery numbers sound about right. In comparison, a new Macbook Air can play 18 hours of video on a single charge. Thirty-five years ago, the Radio Shack Model 100 could run for that long on a set of 4 AAs. It should be possible to make an ultra-low power device that can run the Psion 5 apps (ie simple apps) that can go for weeks on a single set of batteries or charge.

I really miss the Psion 5 / Radio Shack Model 100 / eMate class of devices. I think they are still better in some respects than modern Android-phone-with-a-keyboard devices.