Run time of portable systems is increasingly important as devices become more feature-rich with power-hungry processors, transmitters, receivers, and media playback, to name just a few. Using a battery “fuel gauge” is the natural step to increasing run time of the system. Unfortunately, previous-generation gauges are up to 15% inaccurate, depending on usage profiles and cell aging. This article describes a third-generation technology from Texas Instruments (TI) called Impedance Track, which can provide up to 99% accuracy for the entire lifetime of the battery pack and extend its life.