You could get away with it for a few times but, you are risking a U$100 battery pack and the plane. With the added 3volts, your amp draw will increase to 60+. The easiest and cheapest option would be to prop the motor to get around 40 amps static. Why only 40 amps? Because FMA/Kokam is pretty optimistic with their current ratings. You can also sell the battery and get two packs of the 2000mah 15c batteries @ U$70 each. Two of those weigh ~10 oz and will give 55 amps. Besides, the two packs wil give 4000mah capacity so they will last twice as long.
Fritz
