-JUST READ THE INSTRUCCIONS.
In the Lenovo site the following text is given (at least for the model T23):
"Note: For unattended update, specify the file name with options "-s -a -s". (Example: C:\Temp\1auj20us.EXE -s -a -s) The BIOS is updated without any user interaction."
If u do that u will be able to update the BIOS and the Embedded Controller Program Version without a charged battery and without making any kind of customized bootable disks or something extra.
This worked for me and maybe will be usefull for someone else. BYE.