Del datasheet, parece ser que tenes una señal analoga y no una digital para ser usada por un microcontrolador, es decir podes medir el porcentaje de carga, y de ultima con un comparador (AO) podrias ponerle un LED cuando llegue al nivel que quieras.
Lo del datasheet:
Charge-Current Monitor Output
IOUT is an analog voltage output that is proportional to the actual charge current. With the aid of a microcontroller, the IOUT signal can facilitate gas-gauging, indicate percent of charge, or charge-time remaining. The equation governing this output is:
Vout = 20*(Vcsb-Vbatt)
o
Vout = 20 * (Rcsb*Ichg)
where VCSB and VBATT are the voltages at the CSB and BATT pins, and ICHG is the charging current.
