Not exactly sure what you are saying/asking. I don't understand the "2000m" reference. But, the normal sequence of warnings which begins with red light warnings gives you, depending on your load, between one and 2 minutes before the weakening throttle power begins. If you keep flying eventually almost total cutoff will occur and it will be abrupt.
No sure what is happening to you but the best way to find out I to go out on a test run and just hover in front of yourself, time the flight, and time when the red lights start flashing, when the throttle thrust begins weakening. You could, hovering inches off the round, keep going until power off but that might be damaging to the battery. You certainly want the bird back and in front of you before the throttle power weakens.
If yours is not playing within usual time frames then you either have a bad battery, a bad charger, or a bad bird electronics. A battery voltage reader will tell you what your charged voltage IS and read the discharge level after your flight.
The hover test will tell you whether your system is normal or not, and the voltage tester will tell you whether the charger o battery have problems.
I would recommend sticking with fly fishing....it is infinitely less frustrating.