diff --git a/ESP32/BatteryLevel/BatteryLevel.ino b/ESP32/BatteryLevel/BatteryLevel.ino
index 3abf937..dd5ab23 100644
--- a/ESP32/BatteryLevel/BatteryLevel.ino
+++ b/ESP32/BatteryLevel/BatteryLevel.ino
@@ -15,6 +15,7 @@
  */
 const int MAX_ANALOG_VAL = 4095;
 const float MAX_BATTERY_VOLTAGE = 4.2; // Max LiPoly voltage of a 3.7 battery is 4.2
+const float MIN_BATTERY_VOLTAGE = 3.2; // The system will brown out around 3.2V (undervoltage protection circuitry kicks in). Note that Li-ion chemistry carries very limited usuable energy under 3.2V and will damage the battery with complete depletion.
 
 void setup() {
   // put your setup code here, to run once:
@@ -33,7 +34,9 @@ void loop() {
   // https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/adc.html#adc-calibration
   // See also: https://bit.ly/2zFzfMT
   float voltageLevel = (rawValue / 4095.0) * 2 * 1.1 * 3.3; // calculate voltage level
-  float batteryFraction = voltageLevel / MAX_BATTERY_VOLTAGE;
+  float batteryFraction = (voltageLevel - MIN_BATTERY_VOLTAGE) / (MAX_BATTERY_VOLTAGE - MIN_BATTERY_VOLTAGE);
+  // Battery "percentage remaining" is with reference to 100% being a fully charged battery and 0% being when the system will shutdown.
+  // Note that this is a gross approximation and modelling remaing battery state of charage (SOC) is a much more complicated task done by battery fuel gauge ICs (see https://www.richtek.com/m/~/media/AN%20PDF/AN024_EN.pdf)
   
   Serial.println((String)"Raw:" + rawValue + " Voltage:" + voltageLevel + "V Percent: " + (batteryFraction * 100) + "%");
   delay(1000);