The substrate is below the top layer of glass, so you wouldn't really see or feel a crack in the screen at all. Take a look at
this thread, the top post shows a typical cracked substrate layer and how the screen looks.
I never really checked the longest I could go without a charge, but I read daily and charge no more than every 2 weeks, I'd say more than 3 weeks most times. And that's usually when the reader is no less than 35-40% remaining. One of these days I'll actually check it. But I'm very happy with the battery life on the Glo HD.