My 2s life pack is 1800 mah. I can get 4 or 5 flights on my gasser. http://www.valuehobby.com/power-syst...h-2s-life.html
I know it sounds crazy but I have really been impressed with mine. I am running 5 digital servos and the voltage holds nice and steady. It drops a lot less than the 2s 2100 20c lipo I was running before.
The downside is it weighs 104g vs 29g for the bec pro. Now you are armed with more information... make the choice that you feel offers you the most of what ypu want.