Battery failsafe level?

What is the best way to determine what to set the battery failsafe to?

I am using a 3S and set the failsafe to 10.5V - I only get about 5 mins of flight time, then the failsafe kicks in. As soon as I remove the batteries and check them, they are still measuring close to 12V (tested on 3 batteries).

Obviously this is due to the load…

Is there 1- a way for Copter to account for the battery load?
2- a way to calculate what to set the failsafe to other than trial and error?


1 = No
2 = No

Fly, Chrono, Charge, estimate a possible flight time.
Fly, Check the voltage under load at the end of the possible flight time, charge (if charge is around 75% of the total battery capacity you are spot on). Set your new Failsafe load voltage value and fly again.

Rely on chrono for low performance flight (light wind, low speed). In hight wind or hight performance flight, failsafe is your friend.


On Ecalc website there is a calc tool that helps to calculate real C rating of your battery.

The problem with defective or “tired” batteries is not th etotal voltage but the voltage of the weakest cell.
This is why some telemetry add on use to monitor the tension of EACH cell .

For 30 USD you can but a battery tester connected to your PC to check your battery , it will create a graph of your battery under load.
For bigger battery packs you’ll need to spen more for the tester.