That's one of the things I still miss about my Palm Pilot Pro. It ran on 1 (or 2??) AA batteries, and it lasted a month (seemingly regardless of how much I used it; which is just my imagination, but regardless that's still the impression I have).
The other thing I dearly miss: being able to read it in full sunlight.
The other thing I dearly miss: being able to read it in full sunlight.