Hi Keren,
That is not a TI fuel gauge that you are talking to and I don't believe it has the feature to estimate remaining run time that is found on many TI fuel gauges. For example, the bq27210/bq27010 fuel gauge has several registers to estimate time-to-empty (TTE). Also, the more modern bq275xx fuel gauges with Impedance Track would be even more accurate at this estimation.
A crude way to estimate run time based on the remaining capacity would be to divide the capacity (mAh) by the system load (mA) to estimate hours remaining. However, most systems use constant power (mW) loads as they typically use switching voltage converters. This means that the current consumption will increase as the battery voltage decreases in order to maintain a constant voltage output. The end result is that if you are estimating run time based on a constant current, you will over-estimate the run-time.
The TI fuel gauges using the Impedance Track algorithm will be the most accurate in this case since it can be configured to estimate capacity and run-time based on either constant current or constant power loads. This is what the Load Mode setting is for.
