RE: battery duration
1500MAH battery is 2 1/2 times the capacity of a battery that comes with a flight pack. If your running 4 or 5 servos your good for 5 perhaps 6 flights....remember if you like to gun the engine on taxi, or flying in heavy winds, doing 3D, or the airplane isn't in trim and you have constant stick inputs your battery won't last as long.
If you're that worried about it get an expanded scale voltmeter that puts a load on your batteries and check the batteries after each flight at first...it won't take long to figure out how long you're good for