Page 26 of the manual, “the built-in battery has a capacity of 2600 mAh and a maximum run time of 4.5 hours when using an iOS device and 1 hour and 40 minutes when using an Android device. The remote controller charges the Android device with a charging ability of 500 mA@5V. The remote controller automatically charges Android devices.”
I've drained 3 flight batteries down to approx 15% and still had some to spare in the controller battery on numerous occasions. The controller battery might just have lasted for another flight if I had a 4th flight battery to try it. That's using an android device.