If your carb slide has a return spring or band and the throttle is going wide open your battery may not be the problem. Even though changing the battery may make it appear to be gone the glitch can reappear if you have an intermittent short. I strongly suggest you check all the wires starting with the switch. A run away like you are describing just toasted my buddy's motor for the second time right after he put in a new and freshly charged battery. When I told him to look at his wires the switch was corroded. Also, make sure you check/ re set the fail safes on your servos.