This is a method used to estimate the state of charge (SoC) of a battery. It involves measuring the current flowing into or out of the battery over time and summing these values (a process known as integrating the current). By knowing the total amount of charge that has moved in or out of the battery, one can estimate its current state of charge. However, this method can become inaccurate over time without recalibration, as it doesn't account for factors like efficiency losses or aging effects.