It's not great - generally about two hours of moderate use, and using the backlight a lot shortens that - but the nice thing is that you can carry around a couple of spare AAs and a small plug-in charger
(or even a solar battery charger if you're away from a power source
) and just swap them out periodically.
(Just make sure the backup battery is fresh when you do this.
) I have a 5mx myself, and I assume you don't mean leaving it on for two weeks. Most CE 1 and 2 devices' main batteries will take 2-4 weeks to drain during nonuse. As for the display, it's clear in direct sunlight, a bit less so indoors.
(Adjusting contrast helps, of course.
)