[Skidz]

There is the possibility that the connections from the balance lead to the cells might be a bit suss. I have seen a few forum posts where this has happened (Turnigy and Nanotech). Best way to check is to use a Digital Multimeter and measure the total voltage of the battery after charging. If it reads 25.20V on the meter then the cell is ok. 6 x 4.20 = 25.20V. If one cell is bad, it will be below 25.20V after full charge.

If you don't have a DMM, I can lend you one.