The other reply mentioned that vsync can save battery--on top of vsync, Way of Rhea supports syncing to every other vblank, halving the FPS. This will presumably should save even more battery (though the intended use case is to prevent stuttering on computers that can't consistently hit the monitor's refresh rate.) Ultimately, though, no matter what I do I don't think you're gonna be able to play very long on battery power.

For #2--my glasses prescription is so strong that I spent $330 on fancy lenses today in the hopes that they'll distort less around the edges. Wish me luck. (: