600 milliamp-hour battery should provide exactly that - 600 milliamp hours, give or take depending on battery condition. If your radio system is drawing an average of 200-300 milliamps during flight, you would get an hour or two of flight time. Monitoring my typical 4.8 volt system, I can get a full day of flying on a single charge. There's very little need to quit until your battery voltage drops below 4.75 volts, but again thats dependent on your system. I see a lot of pilots at my field that quit when voltage drops below 5 volts. They're using very little of their battery capacity when they do that.

I've found for the most part, my transmitter battery gives out before the receiver battery.

Brad