Flying 4S after getting used to 5S is a bad idea! Also the graphene additive batteries have a wicked sharp knee in the discharge curve. You can see the voltage drop from 14.5v to 12v in about 20 seconds. Keep in mind my OSD reads about 0.9v lower than reality. Still Dropping a 4S to 9v probably isn’t a good idea! 🙁 Also the tune was a little loose because it’s tuned for 5S, but not bad really.