Pete,
How did you check each cell? If you used one of those $3 checkers that plug into the balance plug, then the checker could be your problem. I just recently used one a brand new Thunder Power batteries and it showed several cells as being bad on several batteries. I got out my multi meter and checked each cell that way. They were all good. The checker was giving false readings.
I'm also running Zippy Compacts 5S 2450ma 35C batteries with no problems. Great performance at a great price.