I remember seeing some battery charging curves, plotting battery voltage vs. time with different constant charge current settings. The higher currents would peak out the voltage and then it would start coming down (which is what "negative delta-v" peak chargers look for). At lower charge currents, the voltage would level off at a maximum and stay there (i.e. not decrease), which would likely fool most peak chargers. I thought you had to get down below 0.1C before the peaking went away, but I guess it depends on the cells your charging.