The bq2010 Gas Gauge IC is intended for battery-pack or in-system installation to maintain an accurate record of a battery’s available charge. 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. NiMH and NiCd battery self-discharge is estimated based on an internal timer and temperature sensor. Compensations for battery temperature and rate of charge or discharge are applied to the charge, discharge, and self-discharge calculations to provide available charge 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 charge may be directly indicated using a five- or six-segment LED display. These segments are used to indicate graphically the nominal available charge. The bq2010 supports a simple single-line bidirectional serial link to an external processor (common ground). The bq2010 outputs battery information in response to external commands over the serial link. The bq2010 may operate directly from 3 or 4 cells. With the REF output and an external transistor, a simple, inexpensive regulator can be built to provide VCC across a greater number of cells. Internal registers include available charge, temperature, capacity, battery ID, battery status, and programming pin settings. To support subassembly testing, the outputs may also be controlled. The external processor may also overwrite some of the bq2010 gas gauge data registers.