The Kindle's virtual keyboard is not suppose to be operated from the serial port or to be available on-screen.
The serial port input from your terminal emulator is the only input device.
The serial port output to your terminal emulator is the only output.
- - - - -
Most likely problem: User error.
See the section you posted:
Code:
Press [ENTER] for recovery menu...
0 /ERROR:gasgauge_battery_id_valid: No battery found
ERROR:
=== BATTERY ID IS INVALID. STOPPING BOOT ===
Does not show you ever pressed "Enter" and is pretty explicit in why the boot process halted.