A multiple energy storage device fuel gauge is described for a device having a power system with multiple heterogeneous energy storage devices. The fuel gauge keeps track of a present state of multiple heterogeneous energy storage devices simultaneously. The fuel gauge implements collective measurement of voltage and current of the multiple heterogeneous energy storage devices via shared circuitry to determine status information, such as state of charge (SOC) and internal resistance values. A controller of the fuel gauge uses various measurements and energy storage device-specific parameters to compute status values indicative of the state of each energy storage device. The status values are maintained by the fuel gauge and exposed to other system components to facilitate power management decisions. A communication bus is used to communicate between the fuel gauge and System components, and a software API may be exposed to facilitate access to various energy storage device specific information.
