A common requirement in battery-powered applications like metering, handheld or wearable products is to know the charge level of the battery. With this information, the system MCU can estimate the runtime and signal when the battery needs replacing or recharging.
The easiest way to get the status of the battery is to feed the battery voltage into an analog-to-digital converter (ADC) and process the data. Scaling down the battery voltage to match the ADC input range requires an external resistor divider. Figure 1 shows a simple implementation.