Originally Posted by TCCPhreak
I guess I'll keep it at the charger for the rest of the day. At least I can see some absolute numbers about voltage on serial output.
When my kindles (k4 and touch) are in fastboot mode and connected to a host PC USB port, the serial port shows voltage levels steadily increasing until they top off at max battery voltage.
If you are not seeing that, perhaps your computer is disconnecting power to your USB port (one of those annoying "green" energy saving things). See if you can disable USB power-save mode in your host PC OS settings or in your BIOS settings.
Or, perhaps you can try a different USB cable...