Not all batteries can pull the same current. A lot of the cheaper packs will sag when under heavy load. My ThunderPower 900mAh pack is a generation 2 lipo. It sags a lot more than my ThunderPower 1320mAh prolite pack. You wanna really start laughing you should see how bad a GWS 1300 mAh Generation 1 lipo sags. Oh man that's funny.
Let's say you have a pack that is 1300mAh and it's rated at 13C continuous and 17C burst. That means the maximum continuous amp draw is 16.9 amps for that pack and 22.1 amps bursting for no more than 10 seconds. Now if you were to actually run that pack at those numbers you would significantly reduce the packs life but the manufacturer says it's safe. Now if you try to pump 30 amps out of that pack it will explode in a heart beat causing your heli or plane to come down in a ball of fire. Do not ever go over the maximum rating of a pack and never run the pack at it's maximum burst rating for more than 10 seconds.
Not all packs are the same. The C rating is only the maximum amp draw that they can handle. It does not say anything about how efficient they are at delivering that power. Here's an example of the TP 1320mAh 11.1v Prolite pack ($55) against the GWS 1300mAh 11.1 v pack ($30) on my corsair using the BP-21 power system. Only difference is the pack but performance is VERY different.
Testing on the bench shows @WOT after 10 seconds with a TP 1320mAh 11.1v lipo on a GWS 8040HD prop
13.24 amps
128 watts
On a GWS 11.1v lipo with the same setup it's much less (crappy gen 1 lipos)
11.43 amps
104 watts
The cheap GWS pack just can't supply the same amount of power.
A Watt Meter is a very important tool to have in your toolbox. I always prop my planes for a few amps below the maximum continuous amps the pack I'm using in it is rated for just to be safe. The blade does not even come close to the limit of the TP900 pack as far as amp draw goes even at hard pull outs.
Someone asked about run times on the TP 900. I'm getting 15 minutes on mine. I don't use the stock TX though and I have my throttle curves set to 100 all the way across the board.
Here's some indoor fun I had a few weeks ago...
http://video.google.com/videoplay?do...65474641347306