The present invention provides method and apparatus for power management of mobile devices and associated mobile devices. The method for power management of mobile devices includes acquiring a predefined battery power level variation Δn of the mobile device and its corresponding usage time t1 if the mobile device uses the power-saving functions; acquiring the same battery power level variation Δn of the mobile device and its corresponding usage time t2 if the mobile device does not use any power-saving function; and determining an extended usage time of the mobile device Δt=t1−t2, and notifying the user of the mobile device the extended usage time. By determining the extended usage time and notifying the user of the extended usage time, the user of the mobile device can have a better understanding of the usage state of the mobile device after adopting the power-saving functions and therefore an improved user experience.