From what I understand Mike, It's not good to try to replace a cell. As the new cell will have a different resistance and will probably make the other cells have to work harder. I'm sure you've read Jim Oddino's info on the Zippy's. I feel the same about running 2 5 cell packs that aren't all matched cells also. The Flight Powers at least give you the option of that if you purchase the matched sets. I'd like to see others like True Rc follow suit as I think that's the way to go. Still, I may have to get some True Rc's as they are affordable.

Chris