Marty;
I have run my 9V QMX on 10.5V, when running 8 fully charged NiMH cells, and the battery voltage would sag to ~9.3V on transmit while outputting ~5W RF CW.
However, even with the voltage sag, I would be very cautious about running it into anything other than a 50 ohm load. I am now using a PD powerbank with a 9V trigger cable, so the TX never sees anything above 9.1V. It runs for days on the powerbank...
72 de Russ va3rr
va3rr