The relatively simple modification to the first-generation Insight involves a shunt resistor, which lets the computer sense the amount of current being drawn from the hybrid battery and delivered ...

However, it also places unique demands and stresses on the active circuitry that captures the small voltage across the shunt resistor—usually on the order of 100 mV—in the presence of high ...

There’s many different ways of measuring current. If it’s DC, the easiest way is to use a shunt resistor and measure the voltage across it, and for AC you could use a current transformer.