Intelligent Battery Sensor (IBS)

It is usually built into the negative battery clamp and talks to the engine or energy management unit over a LIN or CAN line. It calculates the state of charge and health of the battery and helps decide when start-stop is allowed. Without it, many modern cars cannot judge how much load to switch off when the battery is weak.

A precise shunt resistor measures current flowing in and out, and the electronics combine this with voltage and temperature.

A faulty sensor can cause start-stop to stop working, wrong battery messages and incorrect charging voltage. Connecting chargers or jump leads directly to the negative post instead of the ground point can confuse the sensor.