The bq2012 Gas Gauge IC is intended for battery-pack or in-system installation to maintain an accurate record of available battery 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. Self-discharge of NiMH and NiCd batteries 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. The bq2012 includes a charge control output that, when used with other full-charge safety termination methods, can provide a cost-effective means of controlling charge based on the battery’s charge state. Nominal available charge may be directly indicated using a five- or six-segment LED display. These segments are used to graphically indicate nominal available charge. The bq2012 supports a simple single-line bidirectional serial link to an external processor (common ground). The bq2012 outputs battery information in response to external commands over the serial link. 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 bq2012 gas gauge data registers. The bq2012 may operate directly from three or four 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.