Abstract: A method of management of a battery that powers a component of a device may include monitoring a terminal voltage and a terminal current of the battery under a load that is drawing a current on the battery to provide power to a component of the device and modeling the battery as a battery model that approximates a relationship between the monitored terminal voltage and terminal current over at least one of: a certain frequency range; a certain duration, a certain amplitude range, an applied load, a set of conditions of the battery, and a set of conditions of the load. The relationship between the terminal voltage and the terminal current may have a frequency-dependent characteristic including at least two time constants. The two time constants may represent a time-varying relationship between an input and output of the battery model.