Todays electronis are running on 3.3 or 5v and have no room to run more. Basically in any receiver you will find a voltage regulator to controll the voltage but sadly there are plenty of voltage regulators with also an input limit of 5.5 to 6.5v

The most common voltage regulator comes in this package:



Maybe you can open the receiver and find such a component and give us the code printed on it or place detailed pics of the PCB so we can serch the voltage regulator and with that its specification. It is most of the time located close to the battery connector.