How to supply enough power for a DC motor
Total continuous power due to motors running at full speed is say 10 W.

Let's choose a battery of say 7 volts
If motor has to run for 2 hours max, then the battery rating has to be 2 * 10 W hours. 

It is 20Whours.. Or 2857 mAh. 

20/7 is 2.857

So, a battery rated about 2.8 Ah at 7 V will provide you 2 hours of run time for the motor.

Considering conversion losses due to regulator and drooping battery voltage levels when the charge is declining I will ration 30% more.. As my thumb rule.



Unless you run all the motors at peak speed which is doubtful, you will be getting more than 2hours.. What does your device/drone demand finally is the question, just the motor rating alone cannot be considered, I feel.