The top end voltage on a fully charged pack would be about 7.2 volts, without a load on it. As for how low it will go and still operate servos, that would depend on what kind of servos that you are using and how many. If you are using a 2.4, they have a point on the low end of the battery voltage that will cause them to rebind. The servos might still work, but the receiver does not. Good Luck, Dave