Measuring battery voltage on an ESP32

A quick reminder knot with some links related to battery measuring on an ESP32.

https://www.google.com.au/search?q=esp32+measure+battery+voltage

https://www.reddit.com/r/esp32/comments/c7s9io/how_to_measure_battery_voltage_with_internal_adc/?utm_source=amp&utm_medium=&utm_content=post_body

https://fettricks.blogspot.com/2014/01/reducing-voltage-divider-load-to-extend.html?m=1