Many battery monitoring circuits do this, sampling both voltage and current to compute power over time. With a suitable inductor to limit the rate of current ch

Many battery monitoring circuits do this, sampling both voltage and current to compute power over time. With a suitable inductor to limit the rate of current change to be within the nyquist sampling interval of the monitor, you can pretty accurately measure charge going in or coming out of a battery. Combined with a model for the battery and you've got a modern battery monitor circuit.