diff --git a/firmware/sensors.ino b/firmware/sensors.ino
index dc5479f..820650c 100755
--- a/firmware/sensors.ino
+++ b/firmware/sensors.ino
@@ -53,8 +53,12 @@ float fetchWindspeed() {
 // Copied from https://arduinodiy.wordpress.com/2016/12/25/monitoring-lipo-battery-voltage-with-wemos-d1-minibattery-shield-and-thingspeak/
 #ifdef BATTERY_POWERED
 float getBatteryVoltage() {
+  // ESP8266 ADC pin input voltage range ist 0V .. 1V
+  // The Wemos D1 mini does already contain a voltage divider circuit: A0(Wemos PCB) -- [220kOhm] -- ADC (ESP8266)-- [100kOhm] -- GND
+  // The (+) pole of the battery is connected to the A0 pin of the Wemos board through a additional 100kOhm resistance.
+  // The battery voltage of 4.2V max is measured as 1.0V on ESP8266 ADC pin.
   uint16_t raw = analogRead(A0);
   float volt = raw / 1023.0;
   return volt * 4.2;
 }
-#endif
+#endif