CHARGING METHOD AND BACKUP POWER SUPPLY DEVICE

A charging method for supplementarily charging a plurality of secondary batteries accommodated in a casing on a regular basis includes the steps of: charging the plurality of secondary batteries at the same time at the time of initial supplementary charging; acquiring each of peak temperatures during charging of the plurality of secondary batteries; listing combination patterns when the plurality of secondary batteries are split into a plurality of charging groups; predicting, for each of the combination patterns, each of the peak temperatures in a case in which charging is performed for each of the charging groups, on the basis of the peak temperatures at the time of the initial supplementary charging; and split-charging the plurality of secondary batteries in the combination pattern that minimizes a variation in the predicted peak temperatures.