Typically the problem is not that the battery stops providing current it is that the motor draws too much current and damages the battery. This takes a little while to happen (which is why you have a burst rating). Typically when you start exceeding the c rating the battery starts getting host very quickly. When she gets too hot you start to damage the battery. Of course there might be other ways exceeding the current rating damages the battery.

So, even if 18A is the maximum current, but you fly around somwhere between 1/3 and 2/3 throttle most of the time you should be fine. However, if you fly all the time at WOT you may get into trouble.

Like the last chap said, you are probably fine. However, if you are getting into electric models seriously think about buying a watts up meter (or other brands). It's a device you plug inline between the battery and the motor which allows you to read off amps/volts etc. In all honesty, nothing beats actually measuring the setup and then making a decision based on actual measurements rather than speculation.

Cheers,
Oz.