Like aeajr said!

And here's a simple formula for figuring flight times at wide open throttle using 80% of the pack capability. 80% pack usage is the rule of thumb for keeping the pack happy, and providing long life.

Divide the pack capacity by maximum amp draw, multiply that by .8, then multiply that by 60. That will give you what the pack will safely provide in minutes of wide open flying.
Note at reduced throttle the time will increase, but this does give you a good idea of where you stand flight time wise.

Like this we'll say using aeajr's specs above, a 2800 mAh pack and a 28 amp draw system.

2800/28000 = .1 .1 x .8 = .08 .08 x 60= 4.8 So your pack will fly the plane, at wide open throttle, for 4.8 minutes.