I see.. you don’t know if it’s reversed because you aren’t tracking if it’s been reversed or not.
It would only take one more bit as a flag for if reversed or not, but I would copy to useless variable to send.
Code:
useless var word ‘ don’t use for anything other than sending

    IF Voltage = 0 THEN
    GOTO MAIN
    ENDIF
    Voltage = (Voltage - 1)

    useless = Voltage REV 16
    GOSUB SEND_useless

   'pause 50
GOTO MAIN