Characteristically, NiCd or NiMH secondary batteries cannot be charged over a specified temperature, and they can be quickly charged only within a specified temperature range. NTC Thermistor is used to promptly detect the temperature range that will allow quick charging. (*1 in the figure below)
NTC Thermistor reliably detects the completion of charging by detecting a temperature rise of the battery itself (*2 in the figure below). (In addition to this method, the Delta-V detection method (which uses a decrease in the battery’s electromotive force occurring at the completion of charging) is available to check whether charging has completed. However, this method may cause detection errors if the ambient temperature changes during charging.
battery charger NTC thermistor temperature detection circuit
battery charging NTC temperature detection