Yes, this is right. The "nominal" voltage is 4.8. this means that the pack should read 4.8 volts when it has an average charge. Right off the charger, it will read 5.x. it does not really matter if it reads 5.1 or 5.9. After you have used it for 10 or 15 minutes, it should read about 4.8 volts and it should stay there until it is 90% used up. The it will drop below 4.8 pretty quickly to 4.6, 4.4, 4.2, etc. You want to stop using it when it begins to drop. Here is a graph of a typical dischard curve: