A method of estimating a battery life includes: for a secondary battery having a degradation rate R when X days have elapsed after initial charge of the secondary battery, calculating a degradation estimation value (X+Y) days after the initial charge from degradation master data, the degradation master data being identified with use of conditions of temperature T provided for the calculation and a battery state S provided for the calculation; and deriving number of elapsed days Xcorr giving the degradation rate R based on the identified degradation master data, and calculating the degradation estimation value (Xcorr+Y) days after the initial charge from the identified degradation master data.