A battery fuel gauge in a battery management system (BMS) is a very important component that provides useful information about the battery such as the state of charge (SoC), state of health (SoH), time to empty, time to full and available power of a battery pack. It provides information on the remaining energy in the battery, enabling users to understand the capacity and performance of the battery. A fuel gauge ensures that the battery operates within safe limits, preventing overcharging or over-discharging, which can impact battery life and safety.      

The analog front end (AFE) measures the voltage, current and temperature of the battery and provides it to the MCU and fuel gauge. BMS involves cell modeling that simulates each battery cell using a resistor-capacitor network. With the help of such cell modeling and complex algorithms, the fuel gauge estimates the key battery parameters such as SoC and SoH. Thus, the battery parameters are not directly measured, rather it is calculated from measured parameters such as current, voltage and temperature.

A battery fuel gauge in a BMS can be a standalone IC or it can be embedded in the microcontroller unit (MCU). Using a stand-alone fuel gauge IC has the following advantages:

• Efficient Design: Using a dedicated fuel gauge IC to run the complex algorithms allows designers to use a lower-specification MCU, reducing the overall cost and power consumption.
• Improved Safety: The dedicated fuel gauge can estimate the individual SoC and SoH of each cell in the battery pack. This enables more precise measurement accuracy and better detection of cell aging over the battery's lifespan. This is crucial because cell impedances and capacities can diverge over time, leading to runtime and safety issues.
• Faster Time-to-Market: Fuel gauge ICs come pre-tested for a variety of situations, reducing the time and cost required to test complex algorithms. This allows for a faster time-to-market compared to implementing the algorithms in the MCU code.

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