Something is very wrong. Are the servos you are using up to the task? I had to replace my rudder and elevator servos in my Magic for servos with higher torque. The standard Hitec 311's I was using just couldnt do it.
I am using a standard 600mAh rx pack (nicad) and I can fly all morning if I wish before needing to recharge. I have it mounted up on end against the back of the front compartment bulkhead, right behind the fuel tank. The receiver is just a bit behind that up on end also. I am using a Berg 6 rx with the plugs in the end. Makes it easy to plug in the aileron leads.
I had to bend a bit of an angle into the ends of the rudder push rods to make em operate smoothly without binding and at full throw. I keep meaning to replace em all together and go for a pull pull cable setup.

If you are cycling that battery properly and it goes dead in 9 minutes, I would replace it.
Check those servos. Upgrade if needed.
Check for binding. Fix if needed.

Since you are building a replacement, be extremely patient and careful when cutting the pushrods to length. If they are too short or too long, you will be working the servos to death. You want em just tight enough that there is no slop but not to where they are pulling on the servo arms.