Hi Antonio.

I also had the problem, which is why I asked Lou the questions, but I no longer have them. Some things which might help either prevent, or get through, the loss of avionics power.

1. Create a keyboard command for the Avionics Master (on/off). I use CTRL+SHIFT+A. Use the keyboard command to turn the avionics on when needed.
2. If you have a registered version of FSUIPC, you can give infinite battery life to your aircraft by going to Miscellaneous > Extend battery life (indefinitely if value equals 0, else by factor). Set it to 0
3. Add the line electric_always_available=1 to the [electrical] section of the aircraft.cfg

Any of these should solve your problem.