Thank you for the explanation. I did not think it was this easy. But now that I have you, maybe you can help me with the following two additional doubts.
Suppose I plug in two nic-cad 1700ma 6V batteries into two channels of the same receiver through two dedicated swithces (I fly a Futaba T9ZAP with 1024 receiver).
1. Will I need to install also the voltage regulators? (I know that Duralite batteries can shoot up to 7.5 Volts, but also he nics at full charge may go up to almost 7)
2. The two batteries will discharge at the same rate ? Or the second will start when the first is dead ?
3. Don't you think that with usage this amount of voltage will inevitably damage the very thin circuits of the receiver and lead me to an unexpected crash?

I would really be gratefull if you could answare to these questions and I hope you will someday be able to join us for a nice flight in Italy

Ciao