A circuit tracks the total amount of time that a host device has spent in its high power “activated” state (and optionally idle and hibernate states) and thereby can estimate the total power consumed by the host device. A remote device can query the state of a counter storing a value representing this time to accurately determine how much of the energy has been consumed by the host device and how much time is left and/or how many more operations can be performed before the host device's battery is exhausted.