Maurizio Bonfanti ...

^ Can I use, with battery pack BT-13 for TH-F7E, 4 Ni-MH
^ instead 4 alkaline batteries?
^
^ 4 alkaline = 6V
^ 4 Ni-MH = 4,8V

According to the manual the battery must provide between 5,5VDC and 7,5VDC.
So no: 4 Ni-MH (4,8V) will not work.

The external power port (DC in jack) will take 12 to 14,5 VDC so you could
connect 12 NiMh in series to it. Note: this port will accept up to 16VDC but
the transmitter shifts to low power at 14.5 to 16 VDC.

Frank