http://www.amazon.com/Hyperion-EOS-Sent ... 53-7947456
I use the tester above (you can buy a lot cheaper somewhere else, like HK or ?bay).
Since one flies his Phantom with different factors that affect the flight time because the different consumption of the battery power. Yes, the voltage setting in NAZA can be set to suit individual without any other devices but requires some testing.
The factors I mentioned above include: total flying weight, prop size, temperature, altitude of the location (different barometric pressure), humidity, flying style, motors condition, wind condition, battery C-rate, etc.
I set the goal of NOT to use more than 80% of the pack capacity, so the gadget above comes in handy.
As soon as I landed (either by first level fail safe warning or second self landing, up to you but I prefer just after the first level then land), I check the capacity left on the pack. If it is much higher than 20%, say 28% then I know that I still have more flight time left, so I can adjust the FS setting to even lower voltage number. On the other hand if the gadget reads 20% or less, I then know that I have to set the FS voltage number HIGHER or else my pack will not have a long service life.
I also tested flight for the time that is the duration between the first warning and the self landing, so that I have the idea of how much time do I have after the first warning because I sometime fly over water and want to have enough time to bring her back!
At the moment after each flight, all of my battery still have a little over 20% left.
Note also that, higher capacity pack will give you more time between the first warning and second (assuming the same pay load as the less capacity pack). This is also holds true for higher C-rated pack.