Charge a pack up fully. Place it under a moderate load. Measure the voltage across each cell at the same time a load is placed. Cells should measure about 1.0-1.2v each under load. Any cell that is dead will read a non-consistant reading when comparing to the rest of the cells in the pack.

A better solution would be to make the switch now to LiPo.

I've mentioned Flight Power as a high quality brand.

Ryan