[Darthagnon]

Yes, the battery was the issue. I get the impression maybe the battery controllers in the Kindle 4s are not very good - they're supposed to stop the Li-ion from overcharging and from dropping below a certain level, but after seeing yet another Kindle 4 with the same issue, I'm thinking that if left to discharge, they can actually get too low and flip some sort of flag and the screen remains blank. I'm going to try jump-starting this new one, too, see if that fixes it.

EDIT: seems to have reoccurred with the original Kindle. Basically, the battery charge level drops too low, the screen goes to the "plug in to power" image, then when you do, it goes blank and stays blank until the Kindle is jump-started with a higher voltage from a good battery or power supply. I need to see if those metal pads on the back (originally for the Amazon light case) can be used for jump-starting, as disassembly every time I leave them in a drawer for too long is not sustainable.