The bq2050H Lithium Ion Power GaugeTM IC is intended for battery pack or in-system installation to maintain an accurate record of available battery capacity. The IC monitors a voltage drop across a sense resistor connected in series between the negative battery terminal and ground to determine charge and discharge activity of the battery. Compensations for battery temperature, self discharge, and rate of discharge are applied to the charge counter to provide available capacity information across a wide range of operating conditions. Battery capacity is automatically recalibrated, or "learned," in the course of a discharge cycle from full to empty. Nominal available capacity may be directly indicated using a five-segment LED display. These segments are used to graphically indicate available capacity. The bq2050H also supports a simple single-line bidirectional serial link to an external processor (common ground). The 5kb HDQ bus interface reduces communications overhead in the external microcontroller. Internal registers include available capacity, temperature, scaled available energy, battery ID, battery status, and Li-Ion charge FET status. The external processor may also overwrite some of the bq2050H power gauge data registers. The bq2050H can operate from the batteries in the pack. The REF out-put and an external transistor allow a simple, inexpensive voltage regulator to supply power to the circuit from the cells.