A method of estimating battery lifetime includes monitoring a charge characteristic of a battery during a first time period, monitoring an operating condition of the battery, determining a first battery life value for the first time period based on the operating condition of the battery, the charge characteristic, and a duration of the first time period, determining an overall battery life value using the first battery life value and a second battery life value for a second time period, and estimating a remaining battery lifetime for the battery based on the overall battery life value.