You simply over-discharged your pack. A higher "C" rating is desirable, if you can maintain the pack dimensions and weight, if not, you are just adding too much weight to the model. I've seen people running 4S set-ups and the performance is ballistic, but the "C" rating is about the same and the Capacity (2200mAh) is about the same. You need to take better care of those batteries so they last longer.

Rafael