Possible Lipo problem?

Hey guys, ur right, just flattened the problem lipo, with a load the cut-off kicked in, without a load there was still plenty of juice, i drained the battery with no load til cut-off, chucked it on the charger & it read 6.60v, now that i positively know this lipo is to weak for my setup, i have a funny feeling the elite 4800 25C lipo is starting to do it aswell.

I dont know if buying better packs at the equivelant capacity & C rating will help, or i should just go with a higher C rated lipo...