4 to 6 volts depending on which battery you use/
6 volt max and 4 volt min.😊

Around 5v

Thans guys for all your help 5.5v it is then

Just checked my 6CH flysky.

With a battery straight to Rx all channels have same voltage as input battery, used several batteries to test all with different voltages ranging from 5.4v to 6.2v

Using a battery with a BEC the voltage on each channel is limited to BEC output, so I was getting 5.5v.