The likely test would be to watch cell voltages in real time while the car is being driven very hard in sport mode. One would be able to thus get a relative indication as to the variation in internal impedance of each cell. Ones that show voltage sags greater than the majority would be suspect. If they all follow together...you are good to go likely with a very good battery. I use the VX Nano to check on mine for bottom balance but have not yet had anybody drive the car in the aforementioned set up where I can monitor under heavy load. My 14 has been keeping very consistent at the depletion point with the cells tracking pretty close to each other.