simple answer to the "flight time" of the battery. If you fly at FT (full throttle) all the time then your packs won't last as long as flying at say maybe 3/4 throttle
I am doing 10-15 ft hovers and my packs will last me around 25 minutes with my training gear still on. but it depends on what Mah your batteries are how many cells they are. everything factors in.
So in short it just depends on your equipmetn you bought and how aggressive your flying is. My pack is a Thunder Power 1325MaH pack here is one similar

http://www2.towerhobbies.com/cgi-bin...?&I=LXMAG8&P=0