I'm a beginner so double check my advice.

Make sure you use a charger specifically designed for lithium polymer batteries. They are very volatile things. As for charge rate, I believe it's safe to charge at 1C (C=capacity) . So for a 1200mah pack you can charge at a max rate of 1.2 amps. This should help too, thanks to the rcgroups forum http://www.rcgroups.com/forums/showthread.php?t=209187 .