Your book would be correct. The Tx will be somewhere around 10.6 volts when fully charged and the receiver battery will be around 5.3v. Flight time on a full charge will depend on your style of flying. A lot of aerobatic maneuvers will deplete the airborne battery faster than just flying around in circles. Never rely on just flight time alone. Check the Rx battery before every flight with a good expanded scale voltmeter and stop flying when the voltage gets to 4.8