Right now I'm doing a partial refresh, and it manages to last for a couple days but would be cool if it could be unplugged for 2 weeks.

A small solar battery is a VERY interesting idea. If I don't end up being able to hit that number by adjusting the code itself, will look into it.

> for a bus schedule that updates every 60 seconds

Bus stops in Shanghai have e-ink displays that are kept up to date with the current estimated arrival time of each bus. (I don't know what the time resolution is; it could be 60 seconds, but not much longer than that.)