You have made a good observation there, and are probably devdloping questions about the advice you're getting.

It's possible your battery is just fine. You might run the test you ran (4 minute increments, note voltage, repeat) on the ground instead of in the air. After you have mapped your battery response out to an hour or so, you should see how it acts, and at what point the voltage begins to drop rapidly.

That will tell you a lot about your battery and your meter. It should register a peak voltage after charging, drop rapidly to some level, then provide power at a more constant voltage for the useful duration. Then the voltage will begin to drop fast. It is that point, the voltage at which you see the voltage drop quickly, that you should never reach while in the air.

Your meter reading may be somewhat different from the readings you've been told to expect. Good luck, and keep asking questions!

Dave Olson