deli conker,

Your right about the CX battery only being a 2s lipo. The thing about getting one with more mAh's is the size of the battery.
If you notice the stock battery for the Cx is a pretty tight fit to begin with, a battery with more mAh's is usually a little bigger and won't fit. Option B, get a spare battery. You can only expect 10 minutes max from this little bird, it's the nature of this design.

Choppersrule