A battery pack charger includes a first circuit region, a second circuit region, an input voltage measuring circuit, a temperature measurement device, and a controller. The controller is configured to measure an input voltage to the charger using the input voltage measuring circuit, measure a temperature of the second circuit region using the temperature measurement device, and estimate a temperature of the first circuit region based on the input voltage to the charger and the measured temperature of the second circuit region. The controller is further configured to select one of a plurality of correlations between the temperature of the second circuit region and the temperature of the first circuit region based on the input voltage to the charger to estimate the temperature of the first circuit region. After the temperature of the first circuit region has been estimated, one or more control operations associated with the charger can be performed.