So, the first I know that my PRS-T1 reader needs charging is when it dies. This usually happens when I've just got into bed of an evening. Because I'm almost always "in" a book, I never see the battery meter which is visible in the main menu area.
This is non-ideal. I'd go as far as to say it's a bad design decision.
Is there planned a software update where a "battery low" indicator can be shown in-book when the battery drops below, say, 10% or something?
Well, not really. But me having to work around bad UI design doesn't stop that design being bad. Yes, I could press a button every so often. But why should I have to? It's not like this issue isn't easily dealt with by a quick software update.