What is PEAK DETECTION?
When batteries reach a fully charged condition, the pack's voltage begins to drop. A charger that uses peak-detection senses this drop in voltage and changes from a high rate of charge to a trickle charge (or off in the pulse mode). Digital peak detection is more accurate than analog peak detection.
when you charge a battery pack, once it starts to peak , the voltage will start to drop (NicD more than Nimh). As the voltage drops the charger will sense that and terminate the charger according to the threshold you set it at.