I have had two of my kindles discharge so far that it took some serious debricking methods just to get them to charge again. No actual changes had to be made to the kindle. Just trick into into charging (barely) enough to get it to boot to fastboot mode (with MfgTool) when you could get a full recharge rather quickly.
The battery charger is (mostly) software based, and the bootloader depends on the battery having enough charge to boot the device (even when plugged in).
Normal boot mode will power down before the battery is dangerously low, but if you leave it in diags mode, it can COMPLETELY drain the battery in a way that is not healthy for it. I know this from experience (more than once). And the kindle is essentially bricked (by all appearances) in that condition.
