Battery voltages
Please go back and reread what was sent to you in reply to your first message. At any given time your battery voltage will vary between something like 6.8 volts and 8.6 volts, depending on the state of charge of your battery. The exact voltage is immaterial to the power output of the radio, because the radio is probably designed to operate at a regulated 5 volts and this regulation is done inside the radio between the battery's output and power input points on the radio.
The battery seller would do well to state the design center of the battery pack, which is in most cases 7.2 volts DC. Of much more importance, and the thing you should be concerned with, is the current capacity of the battery because that's the thing that will determine how long your battery will operate the radio before the battery needs a recharge.